I just put an Intex unit (bought from KMart on sale for 110$) on my in-ground pool.
To install it, I sawed off the ends of two of the adapters and used fernco adapters. I plumbed it as the last thing on the return line. Worked great, no leaks.
Next, well, concurrently, I added 280 lbs of salt and it worked for a few days and then I got a low salt warning - so I'm off to buy more salt - I don't think I have an accurate volume for my pool whihc has always made things tricky. My best guess (using a calculator for kidney shaped pools) is that it is about 26k gallons.
I have the unit set to run 12 hours a day - not sure if I should have done 2 units in parallel. So far I haven't been able to maintain the 1-3 ppm of free chlorine but I'm going to give it some time, supplement with some granular chlorine and see how it shakes out.
I'll report back with more data by end of the pool season here.