I have a "Pool Miser" autofill and am very pleased with it. After 7 years though the float mechanism was pretty shot from the hard water we have so I contacted the manufacturer about what to do.
They said it required a modified Fluidmaster float mechanism. And that despite looking like the standard toilet part available at any hardware store (for about $6) it was "special". And to boot I had to buy it from my pool store. No direct sales.
OK, so I go order it and in when it arrives it looks exactly like the a regular one. It gets put on the shelf since at the time it was too cold to mess with. So fast forward to a month ago and I'm finally getting around to the chore. I go to the cabinet and without realizing it, grab a regular $6 standard Fluidmaster float (I always have spare toilet parts) and install it. Works fine and I'm happy. I realized my error while looking for something else and discover the $30 "specially modified" item. The mod? No little hose that you attach to the inside of the tank standpipe! I just tucked it down inside the autofill tank and haven't had any issue with it!
So the moral is that you can save money in more ways than just using household chemicals to care for your pool!
Gem of the Blackland Prarie!