I used to do a lot of transfers using TMT 3.1 in an OKI 310.
Always used third party toner as it is, as you say, a fraction of the price. Never had any complaints and the colours were pretty much the same. The only thing I would point out is that the toner never lasted as long as the genuine. I would even go as far as saying sometimes I think I used two third party toners for every one genuine. I have no evidence for this, just what seemed to happen, so it could all be in my head.
Never used third party in my 711WHT but I do not do that many laser transfers these days so will probably keep to genuine.