I got by for many years with a single 13/15 double sided black wrench from Pedro's together with whatever other wrench I used with the locknuts, but a few months ago I bought this set from Hozan because the price was good.

I measured the thickness of the Pedro's wrench at around 1.8 mm, and the Hozan wrenches around 2.4mm to 2.5 mm. Having duplicates and different sizes is nice. The Hozan set is a pair with 13/14 on one side and 15/16 on the other.

As others have pointed out, having individual wrenches with thick handles is probably important if you work on this stuff full time, but for two hours a year the four-in-one set works fine.