I used CarboPlus in my office tank (pressurized gas bottles were not allowed) and they worked just fine. Yes it was more expensive than pressurized would have been on operating costs, but if it made it possible for me to have an impressive moderately hgh light planted fish tank with very little work, so I considered it a good deal. Making a blanket statement that "it is crap" to me sounds like someone who does not know the equipment or how to use it, nor understand that in the real world we cannot always do what our first or optimum choice might be, and that there are always alternate options available. Closed minds are remarkable things, especially in a hobby which should be knowledge-based.
The units are suited best to very moderately sized tanks. They do deplete the KH in the tank while in operation, but if your water is at least moderately hard on KH, your standard weekly large partials will replenish it easily. Alternately you can use aragonite in a mesh bag in a canister filter (I did). It is best to monitor the KH i ntanks where the units are in use, but that needs doing to check the CO2 concentration anyway, so is no extra work.