I have them on a TF F4U 60 ARF, using wire struts. its a 10 lb plane. They are OK once i got the rails level. For whatever reason, the rails are built with a slight curve that follows the wing curvature. The struts are fairly short, reducing the stress on the entire gear system. 17 flights so far.
i used the 615 with robostruts on a 16-17 lb GS P-40 for several years, 150 flights or so. I did have occasional problems, but less than one would think. Not pertinent to your questions but on this same P-40 i have used:
ESM air retracts V1 - lasted 39 flights. part broke, no spares available
ESM air retracts V2 - lasted 5 flights. strut to retract connecting bent beyond repair. much smaller diameter than V1
Sierra retracts - great! obviously the best choice.