I'd be surprised if Burty's are stock, but he still doesn't rate them.
Early USDs suck because almost all of the flex is at the top of the chrome tube, so they bind as they go into the bushes in the upper leg. The 1990 models had mods to increase flex in the upper leg (at the bottom of the lower triple clamp) - the journos of the day didn't get it, but the engineers were trying to move some of the inevitable flex away from the moving parts.
Add in the need to fix the old-school thinking of soft springs and too-hard compression dampening which needs to be fixed, and you're most of the way to the cost of a set of US-spec 46s.
I wasn't until the 43mm USDs arrived in 1992(ish) that USDs were semi-OK. I'd argue that it took until the 46mm USDs came out in the second half of the 90s that they actually were an improvement in suspension actio over the 43mm RWUs from the late '80s.
So... 40/41mm USDs are pooh. Even the '88 KX RWUs would be hugely preferable. I'd hazard a guess that even a earlier set of damper rod forks with some cartridge emulators would be preferable...
