Why would you want it to be reversible?
In case the kit is crap and I immediately take them off

They arrived today.
Fitting took about an hour and a half (despite the drizzle) including the trip to B&Q to get some self tappers and repair washers (I gave in and mounted the ballasts up the side of the lights with a couple of small holes into the bonnet where it's double skinned).
All in all not a badly made kit; the wiring looks good and the connectors are fine but the mounting brackets are a little flimsy. For £22 delivered what do you expect though?
At first I thought I'd been had as neither side worked, but it turns out the connectors to the ballast can be fitted backwards...poor design...nothing to do with me missing the polarity labels. Now they're working though.
Wow, even in daylight the difference from the original lights is striking. I went for 4300k so the colour is very much standard but the intensity is much greater. Just waiting for it to get dark before I give them a proper test.
I was a little worried as the drivers side went out when I closed the bonnet. A quick reconnect of the wiring sorted that so it was probably just a loose connection. The passenger side went out when I started the engine the first time. It came back on when I turned the lights off and on and despite my best efforts with the high beams, the ignition and every possible combination of turning things off and on the problem hasn't recurred.
So far I'm pleased...touch wood...I'll update when I've spent a little time driving with them.