I can see how for heavy secondaries there might be some loss of collimation while pointing in different directions, if the three screws are not clamped down tight enough, so the washer is not sufficiently compressed to hold the secondary holder in position. But this has not been a problem in the telescopes in which I have used this modfication. I wouldn't necessarily recommend this mod for all telescopes, but it can be helpful in some cases.
Chuck
PS. On the subject of rubber parts, awhile back someone mentioned putting small rubber pads under the teflon azmiuth bearings, so that if you pushed on them a little bit, it would flex a little before slipping. I do anything I can to prevent any similar such flexing in my telescopes. I think there is nothing worse than trying to keep an object in view at high power with a set up that has any flex. You give the scope a little nudge, it moves to where you want it, then it springs back to where it was before. Small adjustments are nearly impossible where there this flex is present. The rubber pads are not the only place where flex can be present. The tube and the rocker box are two sources flex with conventional designs, with the rocker box being the worst offender.
I would recommend highly against mounting your teflon pads on rubber or anything else with any flex. I recommend doing everything you can to keep all aspects of the telescope as stiff as possible. Of course, if you have a small telescope used only at low power this doesn't matter much. You can do just about anything and it will probably be "good enough for low power." That is why Coulter can use nylon bearings.