Aric here, Royce's little brother. He and I have been into this since about 1989. Back in the day I played Squats and he played Eldar. I currently have four armies, Templar, Tau, Orks, and a little Guard.
I've always really liked mounted troops ever since I saw Luke Skywalker and Han Solo on Ton Tons in "Empire Strikes Back" I don't think the tau scout would serve any purpose in a game, but the Marine could be a "counts as" bike mounted Captain. I would really like to do a full unit of the guardsmen though. I think the size works well. Any suggestions? They still need paint, mould lines cleaned, greenstuff, etc, but you get the general idea with the plast-i-tac holding their arms in place.