hi jcuk, i have found the eco flow water based dyes pretty good, and the fiebings dyes are lovely,if a little bit messy, to seal colour, you can use a number of things, ecoflow super sheene, resoline, tancoat, to name a few, personally when doing belts, i leave the roughside natural and give it a good coat of neatsfoot oil, and the dyed side i use aussie leather balm, on 3-3.5mm veg tan ,the 2 together give the belt a loely supple feel, and as yet i havent had any complaints about bleed.
regarding the tandy leather, personally i have found the identity store provide a nicer quality leather than tandy,thats not to say what your enquiring about isnt any good, just personal experience hope this helps :-)