The difference is that a pressure balancing valve will maintain your desired temperature when the toilet is flushed, but you may notice less flow coming out of your shower head. A thermostatic valve will also maintain the desired temperature, but you shouldn't note a drop in flow. So if your main goal is a static temp when the toilet is flushed, either will suffice. Mongo

Just finished building my somewhat modest master bath addtion (I did all the plumbing myself). My experience deals with a stand up shower in this particular instance. After some resarch, I decided that I did not need to spend north of $2k on Kohler thermo valve, and I did not need 15+ GPM with 3/4" inlets. By the time I added the body sprays and a couple of shower heads i was in for over $3k which was way over budget. I ended up doing a Moen Vertical Spa. IIRC, I think it was about $1,300 with two shower heads, 4 body sprays, a handheld shower, 5 position diverter valve, and the thermo mixing valve. I just fired it up last week and am very happy with the whole set up. Moen does a nice job, they have some great info on their vertical spa and thermo valves on the moen.com website. It took me a full day to pipe, but I used long radius elbows and took my time to ensure good flow. Having both the pressure balanced and a thermo valve, I prefer the thermo valve and being able to adjust the flow volume. Plus I think it looks better. I ordered it online from faucet.com, no tax + free shipping....plus they price match. If you google the part number and you find a lower price and email it to the price match department and they re-quote the product. Customer service was superb and ended up ordering my sinks, faucets, med. cabinets, and towel/TP holders from them. Again, with no tax and free shipping the net result (to me) was a great deal. I go out of my way to keep from purchasing at the big box - but that might be my personal grudge, but they dont have anything "good" in shower valves in stock any ways, so why bother ordering it from them? Hope that helps.

In my experience with the Bosch Aquastar, the more hot water demanded at a single point of use, the better the unit performs. It can produce about 5 gallons per minute of hot water with a 50 degree temp rise. Pressure balance and thermostatic controls have check valves inside. I think they restrict the water flow a bit in order to find an equilibrium. Tankless water heaters reduce the hot water flow in order to achieve the proper temperature. This feels like less pressure in the shower. Some people install a small pump in line directly after the tankless heater. It is activated by a flow switch to turn on every time the hot water flows. This supposedly helps equalize the hot/cold water pressure.

The ones with one knob, you are really adjusting for temperature only. The only way to get less water is to go cold. I have had a Delta Pressure-balance system with one knob for years. No volume control, really, unless you don't care about the temperature. The only other way to control the volume is to get a shower supply pipe with a T coming off of it for a handheld. I have a valve up there where I can choose the shower head or the handheld shower. If I choose the handheld, I have another valve on that head that allows me to turn the volume to whatever I want. None of that has anything to do with the Pressure-balance system, though. That is still set at the same setting through all of this. My new system will be a Temperature balance system with three volume controls. I will be able to turn the shower head on full, off or anything in between, ditto for the handheld, and ditto for the rain head. The water heater will not support all three at the same time, but we are a house of grown ups and if we try that kind of shenanigans, we will suffer the consequences of finishing with a cold shower! I usually turn it all off to soap up now. I imagine I still will do that, and the rinse will be faster with the rain head. I am hoping to use less water with the new system, with less time fussing with valves.