i would imagine an offset guide would make the handling on left hand turns very different form right hand turns - since in one the rear wheel would cross the slot...
people are beginning to say top tuners will be able to get these bikes performing well on routed tracks, but they are not a good product for first time buyers.
I have seen videos and real life drives of these bikes, box standard, on scalextric track. No they don't move as realistically as the cars, and they have to take corners a lot slower than cars on a well maintained track.
There are 2 points regarding newcomers:
I got back into slots last year, and have no propper memories of my childhood HO set's performance; I was ASTONISHED at the speeds my untuned unoiled scalextric GT40s could do; I was AMAZED when later I realised the back ends of the cars slid and fishtailed like real cars. Now that I know what the cars can do, I find the bikes look very slow. If I had been drawn into scalextric by the bikes instead of the cars, I think I would have been pretty happy with their box stock speed.
Secondly - I have seen a few shop scalextric tracks. These generally have dirty-ish track and cars with dirtyish tyres. Much like a home set if the owner hasn't read up on slot forum about tyre cleaning and track cleaning. The cars on these tracks are SLOWER than the bikes - and I think the same would happen at home, since braids clean the rails.
Ah well, just some thoughts...