As I've mentioned elsewhere on this Forum recently – I've been using an Optivisor for a few months now and I'm very pleased with it. It really makes a difference to what I can see and is convenient in use.
A bit more expensive than your Poundshop purchase I'm afraid – but worth it in my opinion.
I have fairly severe astigmatism and age induced long sightedness so magnifying glasses don't work well for me and I found the Optivisor uncomfortable over my three zone varifocals. At a car boot sale and a local auction I've managed to pick up two Vision Engineering Stereoramic viewers which are essentially ruddy big rectangular magnifying lenses on a big stand. They magnify x2 but one has a supplementary lens that doubles this. They have a wide field of view, high eye relief, and are comfortable to use. One I keep next to my soldering station, the other in my study where I tend to work on fiddly bits. Worth looking for if you have eyesight problems, I paid less than £15 each.