May I add my 2 c ?
First, forgot about the 3 bath kits. If you shoot the latest Kodak of Fuji things, they will give you bad results. (ugly with Velvia !)
1) the Agfa 0.5 l kit is very good but expensive (it's for 4 films only) it comprises a blix so there are only 5 baths (but the 3 more important, say 1st dev, rev, and color dev ) are standard so you are able to tweak them to suit your color balance tastes ....
2) I use the 5 litre one shot Kodak E6 kit.
It is the _real stuff_ but tweaked a bit for the occasional shooter or low volume lab. You can mix as low a 250 cc chemistry to the full 5 litre. And you use the chemsitry mixed one shot. If you're consistent enough in your mixing, results are good and sound. If, as I do, you use a Jobo to process your slides, have a look here :
If you plan to keep the kit for quite a long time once open, split the first dev concentrate in small glass bottles tipped to the brim in order to prevent oxydation. I do this for the color dev also. It is still good after a year. Bear in mind that Kodak keeps two CAT # depending on which side of the pond you live .... The European one I use costs about 55 € a kit.
3) A long time ago, I've tried to mix my own kit, having access to the arcane chemicals needed. It was a total mess. Once bitten, .....
Hope this helps.