...Even if I'd got it for a bargain what is the point if the stuff does not operate reliably ?...
This is where product knowledge pays off big time. My knowledge covers a subset of RTR OO models so won't help you that much, beyond general principles:
Search the net for other owner's experience.
Buy some product that interests you, and has been generally well received
Get to know the manufacturer's technique, both strengths and weaknesses; and find out how you can improve the weak aspects, and rectify problems on otherwise good items.
Major annoyance: manufacturer changes proven satisfactory technique for an inferior one. (May not even be cost down, the 'new way' probably more expensive!)
...In my limited experience diesels seem to run better than steam, less likely to derail, better electrical pick up and greater traction.
The mechanism technique that delivers this superiority from twin bogie traction is common to OO and N and is easily explained.
Structure: a robust casting ensures plentiful weight distributed uniformly on the bogies, and two relatively short wheelbase bogies provide a predictably stable and flexible running chassis with good track holding.
Drive train: a large motor can be accomodated in the centre of the model, with a shaft drive to both bogies, which have gear towers typically driving all wheels.
Current collection: typically available from all wheels, so all the model weight is effective for good rail contact, and the 'agitation' of those wheels by the drive is beneficial for pick up.
This system is so beneficial that I truly wonder why anyone even considers motor bogie drive.
(Sounds wonderful , but there can be problems, as an example in OO, drive couplers between motor and gear tower sometimes slip. Recognising typical symptoms: 'motor definitely running, loco cannot move or only jerks along slowly', 'runs OK in one direction, not in the other', enables purchase of a loco which can be fixed in minutes.)
Compare to steam models (and rigid chassis diesel or electric) there is often less space for motor and gear train, limitations in having sufficient weight well balanced in the centre of the coupled wheelbase; and then there's the drag from any carrying wheels and tenders if present. (It's often the case that a simple 0-6-0T will outperform a much larger steam model for traction, because the 0-6-0T is not having to drag any unpowered wheels around, and plenty of weight may be accomodated in the overall cuboid body form provided by the tanks.)
In HO, Roco power loco and tender using a single motor tender drive, with a shaft coupling to drive the locomotive driving wheels at matched tyre speed. This works well by general report, but not a technique that has made its way into UK product. The technique in Chinese manufacturing is largely derived from North American product. Huge steamers (with shaft drives to both chassis used on mallets) has few matches in UK prototype, it's LNER and BR(ER) alone that you should model to get the best out of it...