Well, they do require more maintenance than a rotary mower. And, they don't mow down weeds that stick up out of the grass, more than 2-3 inches. They just push those higher weeds down, and don't cut most of them off, then they spring back up, in defiance!
And, you have to have somebody sharpen and adjust the "bed-knife" occasionally. The blades on the reel aren't the ones to sharpen. It takes an experienced hand to do that job.
Nice thing about a rotary lawn mower is: One blade to sharpen, a do it your-self job, if you are "handy", and have some tools, other than a bent screw-driver and a hatchet to drive nails with.

How often do you have to check clearances? How often do you have to adjust? How long does it take?

I'm a long time reel mower user, having grown up in Southern California, prior to moving east in 2000. I've owned a succession of Timmers, Tru-Cuts, McLanes, and Promasters. I've even have a couple of Lockes in my basement for nostalgia sake.

You don't say which mower you are considering, nor do you talk about your application. Reel mowers are best for crawling grasses, such a St. Augustine, Bermuda, Zoysia, and other hybrids. Also work well on Dichondra. Also, I wouldn't recommend one for a lot larger than 1/2 acre, assuming about 1/2 again (10,000sf) is lawn. I used to like Trimmer the best, particularly their "Original" model with all chain drive. Many people feel Truc-Cut is better, and I also like then, but prefer roller vs. rear wheel drive. McLane is a decent, homeowners unit, and considerably cheaper, but not in the same class as Trimmer and Tru-cut.

If you are starting with a new machine, with properly sharpened and set up reel and bed knife, you should be good for two seasons before you need a back lapping. If you have sandy soil, you might need to back lap annually. You should then be able to get at least two or three back lappings before you need a full blown sharpening. Sharpening has to be down by a professional, preferably using a relief grind, not the less expensive spin grind. After such a sharpening, the shop will then back lap reel to bedknife to dial in the last couple of thousands, and then adjust reel to bedknife for final set.

As a homeowner you can adjust the reel to the bednkife and you can also backlap the machine your self. All mowers have some kind of adjustment to move the reel relative to the bedknife. Professional machines like Trimmer and Tru-Cut have the reel bearings in eccentric holders, which you rotate to cam the reel closer or further. Less expensive machines either move the reel or the bedknife relative to one another, with a simpler mechanism. The goal is a scissor type action, while not actually having metal-to-metal contact. It takes a fair amount of time, and the reel is set by using a number of strips of paper to see that the ree-bedknife is cutting cleanly on each blade, and at several points across the blade. With a seven-blade reel, you will be testing with strips of paper thirty five or more times.

Back lapping is done using a grit paste (like Clover Compound) to gently grind or burnish the high spots between reel and bed knife. The reel is rotated in reverse direction, and continually adjusted to get a pencil line of contact across the full width of every blade. When you are done, you have to carefully clean all compound, and then set the reel to bedknife as described above.

There are power back-lapping machines or sprocket arrangements, but I don't recommend. They can easily gall the reel and bedknife, if you don't know what you're doing, and at very least tend to remove more metal than necessary. I suggest you get a bell crank, or at least use a large pair of vise-grips to manually rotate the reel. If you damage the reel and beknife with power back lapping, you could be looking at a new $400 reel and $200 bedknife.

Very good information. I have 20,000 sq ft of lawn and I am on Vancouver Island. I believe my grass grass is a blend of fescue and rye so I would to want to cut at less than 1 1/2 or so. I am looking at the tru-cut 25" homeowner model.

Should I stick with a rotary?

20,000sf is a lot of lawn, but since you are considering a 25" mower, you should be OK. You are probably looking at two to three hours when you factor in stopping to empty the catcher, etc.

You don't say new or used. Is this from a dealer or private party? Best would be to try another reel mower, even a smaller one to see how the cut is with your mix of grasses. Rye will tend to lay over which is a problem; fescue is better. On the plus side, you sound like you want to mow pretty close, so a reel is better.

If you like the cut with a reel, then I'd say go forward. On the other hand, if you aren't cutting well, then a rotary with a sharp blade and a fair amount of suction to lift the grass might be best. I use a Snapper Commercial 21" here in Jersey on fescue with good results. It's an older machine (early 1990's but has the bullet proof 2 stroke Wisconsin Robin).

I was going to buy new. I can't find a rental to try so the only other option would be to buy a manual to see how it cuts and try it on a small area. I can't demo from a dealer as there isn't one close and I would buy online as we get hosed on price from Canadian dealers.

It takes me 2 hours now with a 42 ride in due to how fragmented my lawn is. I'm guessing that it would take close to the same with a wider push mower like the one in question.

Once again, thanks for the info and if you think of anything to add, I'm al ears.

Other folks here have already pointed out the downside of reel mowers. The upside, and pretty much the only upside is the scissor cut. Sharp grass leaf cut. Clean, will not see brown or tan dead grass leaf shreds. That's the upside. Most folks couldn't really care less. But golf courses need grass as perfect as can be possible. So, they buy the reel mowers, get clean cut grass, no ripped edges, and they deal with all the negatives of reel mowers.

I used to have a three gang reel (Worthington). After using it for years (with no herbicides) the weeds were taking over. I got rid of it, went back to rotary cut mowers. Many fewer weeds now.

One thing I didn't see mentioned is your lawn needs to be clear of debris like rocks, twigs, etc. Reels down like cutting those things and when they do, you'll find yourself needing to grind a lot sooner. 20k sqft is a lot of lawn. Maybe you could designate an area close to the house where you would use the reel mower and enjoy the benefits. And the rest could be cut w/ the more forgiving rotary.

Why exactlt do you want to get a reel mower?