Challenge: I bought a Challenge and a Challenge Extreme jigsaw as a
distress purchase and both of them went back in short order, the
Challenge because the blade and the sole plate couldn't be set at 90
degrees and the Extreme because it burned out within minutes. Some
cheap brands are surprisingly good but my experience of Challenge is
that they're pretty ropey. But the planers may come form an entirely
different manufacturer.

Black and Decker: I've used several B&D tools and, apart from some of
their older drills, I've found them badly designed, underpowered and
easy to overload. I think there are cheap brands that work better and
are better value than B&D.

Bosch: I bought one of these several years ago and it's the one Bosch
tool I've been happy with in so far as it works and it's done so for a
long time. (I've had drills and screwdrivers fail just outside the
guarantee period - and it's only then that you discover that, at six
months, Bosch screwdrivers have (or had) the shortest guarantee period
of any manufacturer.) But when I bought the planer, it didn't come
with a dust bag (an expensive extra) and the dust port was a
parallelogram shape (why?) which required an expensive optional adaptor
to connect it a dust extractor. If these things haven't changed, add
the cost of the extras into your decision.

Worx: I know a couple of people who've used Worx tools (not the
planer) professionally and they rate them very highly.

Ferm, Wickes black DIY range: I've used both of these and neither of
them were good. The sole plates weren't true. If you Google the group
archives, you'll see this is a problem with some of the cheaper
planers. It's hard to end up with a smooth result when the base of the
plane is wonky. That said, I've seen other Ferm/Wickes DIY tools that
have been good.

The other thing to check is whether the machine comes with TCT blades
or steel blades. Steel blades are cheaper but blunt more quickly, so
if you end up replacing them with a pair of TCT blades (you can find
the price at Screwfix), you'll end up adding £x.xx to the price.

From the list you've given, I'd investigate the Bosch or the Worx
tools.

If you look elsewhere, check the sole plates and the blades.

You'll be better served by a decent planer with a smaller depth of cut
than a dodgy planer with a 3mm cut. And I think the Bosch figure of
1800 rpm is probably a mistake.

Hope this helps.