Nick while I've used a couple of E6 formulae I've found it so easy to do the Reversal exposure method which I was used to from E-4 processing and a horrifically complex Ferrania process about 35 years ago.

If you want to use a small economic E-6 kit I can thoroughly recommend the Paterson Chrome 6
I used these kits extensively in the late 70's and through out the 80's when I used to shoot a lot of live concerts and needed to uprate and push-process my films.

While it's relatively easy to make your own E6 chemistry I found that I hadn't the time to test each batch before processing critical films, hence relying on the Photocolor (now Paterson) Chrome 6 kits.

Nowadays I don't shoot E6, I think the last time was about 4 or 5 years ago. Most of the professional labs near me no longer do R3 or Ilfachrome(Cibachrome) prints.