Per-user pricing punishes exactly the behaviour that makes this kind of system work. A tyre operation needs the fitter in it, the dispatcher in it, the depot manager in it, the owner in it and — increasingly — the fleet customer able to see their own jobs. Charge per head and every one of those becomes a decision about whether the licence is worth it, which is how operations end up with three people sharing a login and an audit trail that means nothing.
It also fits the trade badly. Headcount in mobile fitting moves with the season, with subcontract cover and with the shape of the contracts you are running. A price that recalculates every time someone joins for the winter is a price you cannot budget against.