I have the 30 litre version, and yes I'd recommend them. HOWEVER, I'd also recommend if you do go for one that you also invest in your own malt mill. The holes in the bottom of the malt basket are a tad large, and if you buy pre-crushed you get a LOT of particles going straight through and clogging your pipework up. A mill has other advantages anyway, fresh milled malt for one... lol
As to what size you want, how much do you want into FV at the end, and do you plan to brew full volume or sparge? The pro has an external pump, so can be hooked up to another boiler (so long as you fit a male quick disconnect to the tap on the other boiler) to make sparging easy. I brew full volume in my 30 litre, but only aim for max 14 -15 litres into FV, as there's only my wife and myself drinking the beer, and I like to brew regularly. Variety over volume. I don't use kits, I draw up my own recipes, or adjust recipes from books/the internet, then order accordingly. Kits will mess you up if you are new to AG, or new to a machine, as they are usually designed for a brewhouse efficiency of 75%, which you will not get whilst new to AG, or new to a machine. Heck I am only just hovering around 60% with my Brauheld now, and I had hit 80% with my old setup.... lol You'll find yourself coming in under OG a lot, unless you reduce target volume, and maybe adjust the hops used appropriately also. Less wasteful to just order custom kits, or separate ingredients.
If you don't already own a brewing book, buy one before you get a machine is my honest advice too.
Especially if you just read my post and found yourself wondering wtf I am on about (like I did when I first joined this forum, until I bought a book and read it.. lol).