Ref the FSA rings – following the link, it looks as if they are shaped to match the aesthetic of the Shimano 7900 chainset (sort of …) and are 130 BCD so not a match in any case for a Campag chainset – the “Campag 11s comaptible ” may refer to the fact that Campagnolo space their 11s chainrings effectively closer together (by offsetting the teeth on the inner ring) than do Shimano. Just a guess.
UltraTorque compatibility – you have to be careful about the year, as in 2011, Campagnolo swapped to a threaded inner ring for UtraTorque only – so it may be that which Stronglight are alluding to.
It’s only the compact-pattern rings that use an offset “5th bolt” – standard rings (42/52, 42/53 and 39/52 & 39/53 pairs) did not use the offset bolt, which is there to hold the rings in a fixed orientation relative to each other. The orientation matters because of the way that Campagnolo ramp the inside of their inner ring – the ramping is deigned to work in a very specific way with the leading edge of their own chains – the inner ring has to be able to “let go” of the chain to let the lift pin and ramp guide it up to the outer ring, at a specific time. Hence the orientation of inner to outer matters.
The ramping is more critical on Compact ring combinations and especially on 34/50 because of the big step that the derailleur is trying to force the chain to take.
Manufacturer’s own data shows that changes made to chainring shaping (and stiffness) have most influence on compact-type systems’ shifting and between the “normal” compact combinations of 34/50 and 36/52, the biggest difference is seen in 34/50 as this is where the %age difference in ring size is greatest.
If you are running a KMC chain this won’t work properly anyway as KMC use a different shape on the outer plates and the shaping lacks the chamfer that (in Campag’s case) is designed to mate to the ramps and lift pins. All that will mean is that the upshift won’t work, in all circumstances, as well as it would with an all Campag system. The same would be true in a Shimano system or a SRAM system – all these things are increasingly designed to be used very much as a system, which is not to say that they won’t *work* … the question is, how close to the designed parameters will it work & how much does it matter to you, as an individual user?
On ring prices vs full chainset prices – well, that’s pretty normal. Firstly, chainsets are sold in large numbers and are very heavily discounted – chainrings are more troublesome to stock & to stock control and so are generally not so heavily discounted.
Secondly, in many cases, very cheap complete groupset components are sold into the aftermarket through “grey” channels (they may be OE units sent out to bike manufacturers / assemblers, rather than after-market units, for instance) wheras all spares are sold as AM items and so subject to a different distribution and pricing structure.
Thirdly, spare parts usually appear disproportionately expensive against buying a full item in very many manufactured goods – inventory costs, shipping costs, rate of turnover, the margin required to deal with technical queries around which part suits what and why, all contribute to the final price. When I was dealing with spares at a national wholesaler, we found that complete unit turnover ran at about 15 x the spares turnover … and at the end of each year, our profit on spares was, in effect, sitting on the shelf as stock because of the number of spares that we had to stock “just in case”.