Karl,
The problem with the home-made items, as they are one-offs, and are expensive to make... or they are a bit of a "Heath-Robinson" affair. The MSA is just over £300.
MSA make a robust, simple slide that works very well. All the others I've seen are very fiddly, unlock, lift, latch, pull, slide, latch, then drop.
I assume MSA patents have prevented a direct copy of their simple, unlock, slide, drop.
I'll keep looking.