What's the difference between a regular appeal and an appeal on the point of law only?
A "point of law" is contrasted with a "point of fact." The facts accepted by the court (or not accepted), cannot be appealed now. They can only appeal if the law has been interpreted incorrectly, or the wrong law applied.
It's pretty rare for judges to mess up on points of law, and in this case they seem to have explained their application of the law very thoroughly. It also sounds like an appeal wouldn't be automatically accepted - they have to convince the Tribunal or a higher court that there's a problem before the appeal would be accepted.
I'm guessing this would be pretty expensive again, regarding legal fees. Even attempting to appeal would also be a largely futile endeavor, given that the law is pretty clear and QMUL's arguments regarding the laws have been extremely flimsy.
We need to remember that it is QMUL footing the bill and responsible for going through the hassle of the appeal - not Peter White or the PACE researchers in general. The only reason QMUL took it this far is because White & Co likely portrayed the facts of the situation in a pretty inaccurate manner, and maybe due to the British academic habit of believing everything said by the "right" people.
But now there is a judge telling QMUL how completely stupid their arguments are, so they might value that authority over Peter White, especially when combined with actual rational explanations and evidence. So I think it's very unlikely that QMUL will continue to risk its reputation with even attempting further appeals.