It matters in getting into position. If you can get your str8 sp1 melta weapon safely into a good spot its worth going flat out, plus 3+ cover save is still good.
I like Fire Warrriors I wish I had more painted, I'm working on my third 12 man. For 10 pts you get a str5 30' rapid fire weapon with a 4+ save that's hard to ignore. I think in mass numbers say 6x 12x units it can be a strong army. Granted the rest of your army would probably have to be broadsides