These are around £75 and tracking now costs about £40.
Do they get anyone's vote?
Yes. I have one which I share with my dad. I find it very good and repeatable. Couple of caveats though:
1. ONLY use it with the laser and the mirror on whichever side of the car the instructions tell you to. If you swap them round, it still works, but toe-in becomes toe-OUT (or vice versa). (Don't ask me how I know that..)
2. They're fine for front tracking but for rear tracking they'll only give you the TOTAL toe-in / out. Not per side. (So if you have a back wheel with 1 degree of toe-in, and the other back wheel has 1 degree of toe-out, it will tell you that your total rear toe is "0". (That's how it works on the front too, but of course, you can compensate with the steering wheel)!
3. It can be a bit hit-and-miss getting the angle of the mirror just right, especially on cars with very little ground clearance. There's a bit of a knack to it.
4. You need a flat, level area, although that's true of any wheel alignment equipment really.
5. Doing it with string works if the front and rear track widths are the same. On a lot of cars, they're slightly different. You can still do it with string but you need to set up a string "square" around the car, with the string equidistant from each of the 2 wheel centres of each axle and each string down the side, equidistant from the other. It works, but it's such a pain to set up accurately!