Well, I replaced this: with this:in one of the ground floor tanks today, and from what I can tell, it's working great so far.
Advantages:
1. Much better flow, which was a surprise
2. About a 15% increase in tank capacity
3. Shuts of quickly and completely
4. Quieter
5. Easier installation
6. About half the price
7. Much smaller and lighter.
Disadvantages:
None so far, but the old brass valves did work fine for five or six years, and when it did get stuck, it was easy enough to fix. The plastic valve uses a diaphragm to open and close, which may be more susceptible to debris.
Given the how lightweight the valve is, I may install a mesh filter inside the tank before the valve. Likely this:
I have these before the hose-bibbs I use for the pressure-washer, and they seem to be cheap and reliable.