Don't overlook the stuff Machine Mart sell, and
Halfords own brand are also good value, their pro range has the same lifetime guarantee as Snap On (or they used to, not bought any for a while) but without the idiotic price tag. Good quality Allen keys are a must whatever you are working on, cheap ones will be a bad fit, and will twist and probably round off the hexagon, and you will have no chance of getting awkward bolts out with them. The better quality ones can be ground back when you wear the ends out.
But as others have said, it horses for courses and if you only use them now and again then cheaper stuff will get you by. Mine are Snap On, they cost about £20 for the set of 10 about 30 years ago, and they are the ones that are in a socket so you can use a ratchet on them, and they have been ground back a time or two, but even after all these years they are still as good as the day i bought them.
Heres a tip for getting allen bolts out when the hexagon recess is damaged or rounded off a bit. Use the ball end of a 2lb hammer and hit the top of the bolt hard a few times until the allen key will not fit back in, then hammer the allen key into the hexagon, and slowly try to undo the bolt, doesnt always work always especially if corroded, but will usually shift overtightened bolts. If that fails and you can't get a grinder in to take the head off, then drill into the head of the bolt at a size smaller than the hexagon and repeat the process, the heat generated can sometimes be enough to loosen the bolt so you can get it out.