As regards point (a) above = unwanted uncouplings, I found this very helpful post on another forum (top post on this page http://www.rmweb.co.uk/community/index.php?/topic/48728-dapol-easi-shunt-magnetic-couplings-in-n/page-14) as follows:
Benn wrote:Hold the pin with a pair of tweezers and gently rotate it, it should move easily enough to the correct position, and it's sometimes worth a little play about and adjustment sesh to get them to operate that little bit better. I've found a reasonable improvement in operation and reliability can occur by putting a little 'drag' on one axle of each vehicle that has the couplings attached, I've used some spongy laminate flooring underlay and just sandwiched it between the centre of the axle and the top of the bogie moulding, and stuck it on with a bit of bostik. The vehicle now doesn't roll away or move when being coupled/uncoupled, and also remains tensioned to the loco when being hauled so when passing over the magnets it doesn't auto-uncouple when you don't want 'em to!
So I had a session bending the pins outwards to reduce the likelihood of the couplings opening when not wanted, but I still had problems - some wagons were fine, others not. So then I tried adding a small piece of foam under one axle to increase the drag on the vehicle.
IMG_2488 by PinkNosedPenguin, on Flickr
Not pretty underneath, but invisible when on the track of course. This worked amazingly well It ensures the couplings stay 'in tension' when running over a magnet and have so far totally eradicated unwanted uncouplings Intentional uncouplings are not affected and are very reliable. It also has the happy side effect of making coupling-up nicer - you can just gently nudge up to the vehicle and couple up without having to give it a 'big bump' - again the extra 'brake' makes this work better. As I will only run short trains on my layout I don't think I'll have any problems with pulling the rolling stock, even up my future incline. So thanks to Benn (and I think Karhedron suggested this too) for such a simple, cheap and effective solution to this annoying problem. Unwanted uncouplings are so annoying and embarrassing its so good to avoid them! Hands-free shunting is a bit of a revelation in N gauge, but is now a reality.