I was tempted to post the styx story. Like any organisation the AAIB does good work and 'less good'. There will be highly competent people and those 'much less gifted'.
For GA incidents, in the general scheme of things there are considerably less important than CAT, so where do you put the really good people? That frankly is simple good sense, so many of the impassioned pleas "wait for the AAIB report" will mean the result may not be that impressive. Especially for those accidents where the only commentry comes from the pilot and given human nature they are unlikely to 'fess up to gross incompetance!
In this case, from the pictures and comment, it seems to hardly need detailed investigation, clipping trees on the approach should be something that simply does not occur during VFR flying. So that leads to a pretty obvious answer - whether the engine was running or not I'm afraid.