I have not purchased the Harbor Freight vent openers, but in past threads here they have gotten uniformly poor reviews. Here are a few threads that might help:

Automatic vent opener brands

Harbor Freight Vents

I don't have an HF greenhouse but I have used the openers on my self-built PVC greenhouse. One of the original two is still in service after 3 years. The second gave up the ghost late last year and I replaced it. It seemed to have suffered a lot of corrosion, perhaps due to my frequent spritizing of a plant that is no longer there (that window is on the lower side of the greenhouse--I used a little pulley and counterweight to act as a tension source against the opener since they are not designed to work vertically).

I know someone who agrees with the bad reviews and would not use them, but for me the price and--so far--durability seem a good compromise. If I were gone for extended periods of time (as my friend is), I might rethink that.

i HAVE A HFGH AND HAVE HAD THE AUTO VENT OPENER THEY SELL. iT ONLY LASTED 1 1/2 WEEKS. DON'T BOTHER WITH IT. i WOULD SPEND A LITTLE MORE MONEY AND GET ANOTHER BRAND. I BOUGHT ONE WITH SPRINGS ON IT AND IT'S WORKED BEAUTIFULLY. THE HF IS TO FLIMSY AND THE FLUID LEAKS OUT AND THEN IT'S DONE. i LOVE MY HFGH W/MODS. i'M THINKING OF GETTING A SECOND ONE AND ADDING ON. CHEKC OUT EBAY FOR THE OPENERS.

Thanks folks for your input! I've purchased 2 of them & I'm getting ready to return them. Just can't seem to get them to work........ Tired of fooling with them. Guess I'll check out other brands........ I really would like to use some sort of opener.......

I have had good results with this opener HF #92192. One of 4 did leak after 3 years, and I would like to know what the fluid is. It seems like mineral oil. The cylinders are easy to disassemble, and it would be good to know what to refill them with. Anyone out there knows what to use?

I have no experience with HF, but do with Riga's type. They are supposed to be strong, but are no match for the winds that we can get here. Last winter in a blizzard, somehow one snapped the aluminum strapping we had anchoring them down with inside and flew straight up in the air and was battered by 60 mph winds for about 24 hours. Thank God no structural damage that couldn't be fixed, but this year we replaced them all with GigaVents. These bad boys are beefy! You may get some idea from this attached pic. Got them from Peaceful Valley Farm and Garden Supply ... little spendy at $129 each but worth the peace of mind.