The two main issues I have with them are that firms tend to give them to just about everybody (instead of just to folks working very directly with real IP), and they only pay base salary, not something closer to actual total compensation (often multiples of the base pay).
Having said that, the quant firm is relatively unimportant and not a good reason to prevent a total noncompete law. It's probably better to just ban them then try and make allowances that aren't full of loopholes.
But for SW devs, the non-competitive agreements in Finance industry isn’t really the same kind of bondage as for Quants. If Quant changes company - his options are very much limited to other companies doing trading, thus directly covered by non-competitive agreement. If SW Dev changes the company - he can choose the company working in other industries not related to finance, and then he is free as a bird.