Is there a definitive guide to Pentex Lenses

I obviously haven't got the hang of AF yet then.

I find pointing the camera accurately enough for the AF to see the bird (obviously, only if it's flying... ) and focus on it (this is at a minimum of 200mm) harder than I do focusing manually.

If I miss it a bit, the AF hunts, the whole thing goes way out of focus and I can't see the bird any more either. Much easier so far, to follow-focus as I pan.

Any hints for better AF technique?

I would steer clear of those. I have no direct experience with this lens, but my experience of cheap long zooms is that they are cheap for a reason. Also F6.7 is technically too dark for AF to work. In fact Pentax tend to under promise and over deliver with their AF so it probably would work most of the time, but it wont be fast and will probably hunt quite a bit. You would be much better off with a Pentax 80-320 or a Sigma 70-300 APO (note the APO, it's important).

I think that's the main benefit of multi-point AF ie. hopefully one of them will lock onto an off-center target.
Fast moving subjects and especially those that are fairly small in the frame are always going to be a challenge for AF systems, no matter how sophisticated they are or how quick and accurate your aim is.

If absolute focus precision isn't the priority but you do want to maximize the number of reasonably successful shots, it's probably best to switch to manual and use hyper-focal focusing