It is a good idea, but the problem is that they often don't work on tyres for two reasons:
1. The margins are very low, so the savings are very small (sometimes only £10 per tyre).
2. Very few people are prepared to buy a set of tyres in advance of when they require them and store them for later use (especially if there is little financial incentive to do so). In the absence of that, you are reliant on finding enough people who want tyres now.
Also in terms of the R35, few people have reached the mileages necessary to require new tyres.
I'd be happy to participate, but then I once bought a dozen 315/30/18 Corsas from Tirerack in Ohio when they had mid-winter sale at $165 each! Even airfreighted from US, with taxes etc it was half the UK price!