Didn't even know Lidl did welders magnets; will have to have a look for them.
I've got 4 little ones from Ebay; only used the one and liked it so much I ordered another 3, so much easier than trying to balance things or clamp with the return clamp which is what I was doing before.
These are the ones I have; I like them because there black so are easily identified of mine when welding with others and the small size and relatively strong magnet are ideal for smaller tasks. Will get some of those from Lidl when I can for bigger tasks.
Don't know how long it lasts, but all of the makers I know use Titebond 3 for outdoor applications. I used some recently, seems to work well, but it's quite runny and takes longer to go tacky than the indoor products, if you're gluing a large area I'd recommend using a sponge or glue brush to spread the glue out.
First half of top getting glued and clamped. Brushed glue on like ya suggested Yamhon. Using frame its for to glue on as it allows ya to clamp down as well as across, unexpected bonus