Interesting DJ
Looks like you are having the same experience I did
The 7's I had were well made and the hoofs gripped well but I could bottom them out of the box
To me it sounds like your brother is bocking on stilts that are too higher weight for him and the 7's are a bit softer so give him a better time (I had the same problem when I started) and as soon as I dropped down a couple of Kg I got loads more height and my confidence went up
The only other problem we found was that the hoofs on one set started seperating from the ally frame (the rubber started to split) so will be interesting to see how yours fair after a 6 months or so
Nice to see a set of 7's again as they were everywhere when I started but now you see about 1 pair a year and they are at least 2 years old
Jason