I've seen the kind of wheels you refer to, and they look good. I'd have a few questions about 'em, though.
O-rings are used primarily because they are readily available today, whereas rubber in the form of an idler wheel has to be manufactured. Obviously, using something ready-made is much cheaper. It is cost, not performance, that led to this --but that alone does not say that the performance is better or worse than the original design.
A clever DIYer tried an idler wheel, found it worked, and the idea has caught on. As far as I can tell, few if any serious A/B testing experiments have been done to see which might be better.
Is the contact area really that much smaller? O-rings are typically supposed to deform slightly to create seals, and so most commercially-made O-rings are made with much softer rubber than than that used in idler wheels. If there is more deformation at the point of contact of an idler wheel, the actual contact area may be similar to, or even greater, than that of an original idler. Some of the idler-wheels I've found had beveled "knife-edge" contact areas, which, especially in a harder rubber, could form even smaller contact areas than an O-ring. But many of the older idler-wheels have been worn down from years of use, to where they have wider, flatter contact surfaces. Clearly, these could be worse.
That said, the softer rubber of many o-rings may wear over time in a similar fashion. You might well end up having to replace the o-rings more often than you'd have needed to replace a harder-rubber idler wheel. But o-rings are cheap and easily replaced, so this shouldn't be a big problem; it's on a par with replacing belts.
I have seen some with THREE O-rings being used: two side-by-side to form a base, and one between and atop them, which actually makes contact with the platter. Such a design would do more to isolate vibration, but it might also introduce a wee bit more speed instability(?)... but any such instability would still be much less than that from a belt, and could probably be entirely discounted.
Better (more precisely made and smoother) bearings should, indeed, be an improvement, allowing for less bearing noise, less bearing-induced vibration or instability, etc...
The materials from which the wheel itself is made (types of plastic or metal) of course will affect the manner in which vibrations pass through it. In an idler wheel, one ideally wants something entirely rigid, but which stops all vibration from being transmitted through it. No material does that perfectly. Something like DuPont's Delrin might be superior at this, but metal is a more practical alternative. Using two metals in the construction (with the addition of bronze for the bushing/bearing sleeve) might tend to lower the transmission of vibration, in comparison with using a single, solid metal, but the exact effects depend upon the specific materials and which frequencies one is considering.
In practical application, people using these "newfangled" idler wheels seem quite happy with them, and I see no major problems (and some advantages) with them, so I'd say go ahead and try one. They won't be bad, in any case, and at least in some ways (better bearings) should be better. Plus you'll get the convenience of easily-changed O-ring construction. But whether they are fundamentally better than the original-type designs remains to be proven, I think.
