It's certainly a very worthwhile improvement over the original game. Interesting that he stuck the code in with the graphics data for the front screen. Presumably, he didn't have the benefit of the Skoolkit disassembly showing him where all the unused areas of memory are.
Do you know if this one also patches the two attribute buffer copies as well as the pixels? Turbo MM and JSW both do this for an additional gain.
Doing some quick testing by timing the number of seconds it takes poor Willy to asphyxiate when the air runs out, the original game, with the music off, times out in 2m 21s. The version above ends after 1m 43s. Turbo MM in 48k mode is good for 1m 31s and 1m 22s in 128k mode.
There is a second or two still up for grabs for the 128k mode and I will eventually get round to doing it. It won't be too noticeable when playing it, but it'll make me feel good knowing that it's in there...