These sliders should be pretty universal in regard to gameplay speed. I would expect them to play well on slow speed.
I adjusted them on normal speed, but the base set I tweaked came from Armor's v1.2 set (which came days after release), and he played on slow speed while adjusting those, so you should be fine playing on slow. I'm not 100% sure though, but my best guess is the sliders should translate to slow speed as well.
Hope they work just as well on slow, and I'm glad you like them.