Yeah the MTB ones work fine for road bikes. The only issue I've seen is with track bikes or road bikes with tiny clearances between the front wheel and the downtube, then you should use the fender version of the steadyrack.
Tarmac is probably the "closest clearances" so I assume that would be fine. I've watched the video of the guy building his own monorail hook setup and now I'm curious about that as an option. Not sure about drilling stuff into my roof though.
I've seen a Tarmac with a scratched downtube from a steady rack. I would advise you to get the fender compatible. It fits everything up to around a 2.4" tyre but has much better downtube clearance.
Yeah the MTB ones work fine for road bikes. The only issue I've seen is with track bikes or road bikes with tiny clearances between the front wheel and the downtube, then you should use the fender version of the steadyrack.