I used one of the Smart 40 quid ones for a year or so when I cycled regularly on an unlit lane. I found it good on the whole. The lamp optics did cause a strange halo and the bracket can be a bit bouncy. The battery hangs over the top tube (on a diamond-frame) so it may not suit all bikes. The four options of the two lamps being on or off are selected by cycling through a single switch, I'd have preferred two independent switches.
I now have a single-light Cat-eye system with a bottle-holder battery, this was used to supplement a hub-dynamo driven light on unlit lanes. I prefer the bracket on this one especially as it is the same as most other Cat-eye brackets and so I can move lamps between bikes. This one is around the 40 quid mark but it doesn't appear on the SJSC site.
They are fairly basic. I have a set an am happy with them. But, they do have some drawbacks. The mounting is fairly 'floppy' so the beam jumps about a bit and the lead acid battery, while cheap, is big and heavy.
If you want the dogs danglers of lights then these are not it. If you want a set of lights that are OK, strong enough to light up a country lane or track, sufficient to make the oncoming cager dip his lights and cheap & cheerful then these are OK.