They're fine for MOT's in the UK. The Lens etch does not affect the beam pattern what so ever. The light output is also not affected at all as long as you don't go overkill with the etch design (i.e. etch too much of the lens). Even then the affect on light output is minimal to the point it isn't really noticeable.
Just to reference the relevant MOT test criteria:
4.1.1. Presence, condition and operation
You must test all mandatory headlamps.
‘Mandatory headlamps’ are a matched pair of main beam headlamps and a matched pair of dipped-beam headlamps. These can be separate or a single pair of headlamps.
Lamps are matched if they:
emit light of substantially the same colour and intensity
are the same size and shape that they are symmetrical to each other
This section is talking about having matching pair of headlamps, i.e. having having 1 xenon headlamp and one halogen headlamp for example would be a fail under this section.
Also covers having matching headlamp bulb temp, more relevant to xenons.
section 4.1.2 is about headlamp level and beam test, which these are compliant with as they don't affect beam patterns
Rest of section 4 isn't relevant (as it covers the operation of headlight switching, auto levelling and headlamp washers etc).
So basically there's only 2 things relevant in the MOT test criteria, 1. light output and 2 beam pattern which isn't affected by custom etched lenses. There's no reason to fail the lights for custom etched lenses
Tinting the headlights would have a far greater affect on light output when it comes to MOTs than this
Some good info on it here:
https://www.youtube.com/watch?v=A9DDEvX_044
Just finished the custom headlights for our Kuga with custom etched lenses today so will post some pics up of that soon including the beam pattern