Originally Posted by corporate-wage-slave

You probably need this FAQ more than my advice.

I've only done DONE - the business class version of the Oneworld Explorer, which is different to the Global Explorer. I haven't bothered to upgrade segments (unless they get offered...) so this is not personal experience. However you apparently can MFU DONEs sectors but not LONEs, the Economy version. You would need to buy directly off BA since travel agency tickets are generally not open to MFU.

For Global Explorer you can pay £550 to upgrade a sector from WT to WT+ and OW equivalents, or £850 for very long sectors - there's something similar with OW Explorer. So I suspect it follows the OW Explorer logic and you can't MFU from WT.

Personally I think OW Explorer is good value, Global Explorer less so, but of course YMMV.