I am looking to buy a Bec , but not sure about buying one with a reverse box people seem to think they are unreliable is this true?

They dont have a good reputation.

Tend to be noisy if you can hear it over everything else. They get hot and throw oil out through breather and eventually the bearings fail. One owner got around that by extending the breather up to the top of his windscreen and put a resevoir there. It'd slowly fill up but drain back when he stopped. Ugly but it worked.

They're not a good thing, situation stated above is very real.
Electric is really the only sensible option, rather than just getting out and pushing it. That latter solution is a pretty good one, until you meet the usual 'me, me, me' motorist down a single track road.
Electric, either off a gear somewhere on the prop (differential end the usual) or a ring gear on the sprocket (chain drive cars).

If you buy a car with a reverse gearbox, it's easily deleted with a new propshaft and a Transit bearing where the box was.

Don't even think about mixing anything mechanically reversing with high powered BEC engines, slick tyres and racetracks.

Feels like a thing that should be super simple. Shame the target market is so small it doesn't make anyone willing to make a proper one. In reality it's total overkill when electric is lighter, simpler and cheaper to make.