I think custom work out a bit better overall due to quality of parts. Better waterblocks, better (quieter) pumps, that sort of thing. "Do everything" or all in one combo type products rarely work as well as individual parts. Kind of like getting an all in one tool that's a mower and an edger and a leaf blower and a hedge trimmer. If those products truly worked as advertised or were as good as individual higher end equipment then landscapers would be using them. Kit's are usually cheaper and all about convenience. It does cost more though, just like individual tools cost more. Plus you get customization options you wouldn't have otherwise, with an aio you're limited to tubing length. Custom loops you can build out and arrange parts where you like and they will still reach.