IMO the BMW charger is unnecessarily complicated (and therefore expensive) simply because of the complexity of it having to operate in a canbus environment. The solution of connecting a charger, or indeed any other accessories directly to the battery (and there are a number of ways in which that can be done), removes that inherent complexity. It therefore becomes a simpler solution - one that also permits other accessories to be connected, again, in isolation to the canbus system. I have this opinion based on my own experience of circumnavigating around canbus complexities with regards to fitting other electrical items to my canbus bike. So, in my opinion, the £5 lead for an Optimate is a far better solution that buying the BMW charger for £80 even forgetting the price differential.