I have one for my 75 it's a used one and it was my first ever regulator. It's been working pretty good for me so far once I learned how to properly adjust the bubble rate. My bubble count has been pretty constant too. It's not a bad regulator for its price.
I've been using one for a year with decent results. These units are sorta like a first car.. It'll get you where you want to go, but it'll teach you what you really want out of your second one. I'm getting ready to replace mine with a rig I've built.. better needle valve was at the top of the list for improvements..
I started using one of these recently. It seems fine. Make sure you follow the directions in setting it up. I haven’t been using it long enough to know how it weill work in the long run but I had no trouble getting the bubble count I wanted and keeping it constant for the last month.
Your gonna see some hate on here for the MA857. Is it the greatest no, but it does the job for most people. It's been around forever and I don't think it would still be out there if i was that bad. Many of the issues posted here are people who bought used ones or people who never used a co2 regulator before and damaged it. As BruceF noted, make sure you follow the directions and if you don't understand something don't guess.
BTW I've used them on all my tanks and never lost a fish due to a malfunction.
I would say this , get a bubble counter with a Check valve, the bubble counter that comes with a M957 doesnt have a a check valve with the bubble counter n is some cases i heard water getting into the solenoid because of this...
Thanks to everybody for you input. It did take a day to settle down and now lets see how steady she runs. One other question, How many bubbles per a minute for a 25 gal would put me in the ball park? I had a red sea pro set up years ago and that let me down after a year...