Pierre,
The HRIIs and my S-6 have Harmon Titanium struts. They are longer for more clearance for the longer props on the 540s. I've actually found them to be a bit more forgiving than stock RV struts.
Not spongy or springy, but just a bit more forgiving...or "absorbative", if you will. It's not a major difference from RVs in feel, but slightly noticible. I've found this to be a bit more apparent in the HRIIs I've flown...ever so slightly. Mark's F1 felt very similar to my plane and the HRs I've flown. I would not call them stiff legged, though you can bounce them just like an RV if you drop it in or drive it on to soon...Rockets and RVs don't feel all that different there. Rockets and Supers feel good 3-pointing or wheel landing, whereas 8s seem to like wheelies, and 4s seem to prefer 3-pointing (and that is just a personal assessment from a little time in each, and some discussions with others...and probably a bit of hamfisting on my part too!
)
Paul Dye just flew my plane, so he may be able to comment on the comparison as well. Smoky, Mark, Tom Martin and other RV/Rocket repeat offenders will be resources as well.
There is a Rocket for sale at Stead, if your buddy is looking for more prospects!
Cheers,
Bob