That's a pretty good deal. A typical three-hydrometer brewer's set would run closer to $100 (example
), though as Tom mentioned those would have thermometers and correction scales. Assuming the quality is decent, my other concern is that the ranges aren't really set up well for beer. The professional models cover ranges of about 8°P, from 0 to 24. The ones NB is selling are 10, 17, and 16, give or take. They go way above and below the practical range, sacrificing precision.
So while the price is right, if I was set on committing that kind of money to a precision set, I'd pay a little more and get the real deal.