I think @OwenWatson is interested in what other brand may be suitable instead of Deta.
Never had taking the plug lead out of the terminals voiding a warranty on any product I've ever had to return. As for the pricing argument, aside from the RCD specification, you'll find more people will complain about HAVING to spend that little extra on a plug for each light as they've spent bugger all on their downlights.
I've only had problems with terminal sizes on some extremely overpriced fittings specd by architects - could only fit 1x 1mm cable in! The rest I always manage
As for 1 in 30 failures mentioned above, there are some bunnings and the like fittings out there I've had to go and take out of brand new houses (supplied by owners of course) because they've melted / have fire risk. Just not worth it. Even if they'll pay all the bills associated with the repair, there were instances where painters had repainted ceilings after lights had gone in and there was paint damage getting the old ones out and the new ones in. Absolute pain having to get entire open plan ceilings repainted
Don't tend to get that with the likes of Switch lighting where you might spend a bit more but I've put thousands in and not had one faulty yet over the last 7 years I've used them