Actually, it won't be on the 767 (2 - 3 - 2 ET, 2 - 2 - 2 CE). The configuration switch is achieved solely by expanding the left and right seat of the middle section inwards. Nothing expands towards the aisle, hence no need to avoid a safety hazard when the curtain is closed (which is why the first row of economy is in business configuration on planes where seats are expanded towards the aisle, in BA's case in 3 - 3 vs. 2 - 3 configurations).

My own advice is to go for the back of the bus if you value an empty seat next to you - BA fill their planes from front to back. I prefer an empty seat next to me over additional seat pitch (at least for short flights) - YMMV.