The Victron Blue Solar 15A unit is a nice one and very good value for money.
It handles 200W of solar wirh a 12v battery and is best suited to a 24v panel ( 72 cell). It will handle up to 36v nominal in.
It will also work on 12v with a nominal 12v panel ( 36 cells) but I wouldn't use it that way.
It does current limit sharply at 15A and gets rather hot when current limiting, probably ok short term but can't be good long term.
In poor light conditions you can run up to about 300W of panel but under good conditions it will be close to current limit with 200W. It is a 200W device and if you have too many panels I would run 200W via the controller and any excess direct.
There is a bigger one that I wouldn't touch, it uses the same voltage panel as the battery ( 36 cell at 12v or 72 cell at 24v) this is not then best way to run things and does nothing for the cable I^2R drop and doesn't give the best match.
I would buy more than one 15A unit rather than any of the more expensive 30A units at a far higher price. When you get over 40A then is the time to look at Morningstar, outback or classic,
where you can justify the cost but for the small end I like the Blue Solar 15A. I really have no idea what the Chinese things are like , some may be ok, othere are certainly crap and until you get it you have no idea what you will end up with.
Flux