I've been using them for 3 months now and really like them. I top water my smart pots full of pro-mix HP with 1/4 strength nutes every watering, plain water every 4th watering. I just don't have the space to do a proper hydro set up. I do have a PH pen, and the Ph perfect seems to buffer my tap water down to 6.4 pretty consistently.
Mind you I don't keep a standing reservoir of nutrients, so I can't speak to the long term stability of the buffers.
BC, I got my 3 part set ( 1L each grow,micro,bloom) for around $30 at my hydro shop. At the rate I'm going, the 1L containers will last me until the spring at least. Then I think I will upsize to larger containers since my peppers seem to love the stuff