Not sure if the SP mk2 & r190 is considered crappy or not. But as an O2 reg I like that its moronically simple, tolerates flooding, its almost impossible to have IP creep in that unbalanced piston, and there's no diaphragm to tear or fail. Basically if all my other regs are shot to hell, that one, while not as smooth breathing as many - will work. It works at 70ft for 50% too, but I notice the slight increase in cracking pressure.Same here ... why would you pick a low quality reg for the potentially longest phase of the dive? Even with a good reg I always dislike the feeling of the first few breaths when changing from 18/45 to 50% and you really feel the different work of breathing ...
Btw the crappy deco reg is similarly flawed as picking a crappy reg for you backup (which you would want to be nice in that moment you really need it).