Ive got a clarke one, dont know the model number though. Looks like this though so I assume its the 24
http://cgi.ebay.co.uk/CLARKE-CIR24-2...-/400162502542

Ive never needed the second battery during a trackday yet even when Ive changed the wheels a few times, although I tend to breaker bar them first just to loosen them as IME the main thing that kills the batteries is when they are sat there hammering away trying to get the nuts to crack in the first place and likewise if you sit there hammering it to tighten, so if you just give them a quarter turn with a bar first and use it to do the final tighten they just seem to last and last.

Mine is so good I use it all the time at home as well even though Ive got the compressor sat there, just cause its easier than messing around with the airline all over the place, I use it for stuff like subframe bolts and things not just the wheels, I cant believe how well its lasted consdering the amount of use it gets.
If mine goes wrong, i'll definately just buy the same one again TBH, does everything I need quite happily and the batteries charge very quickly too (about an hour IIRC)

Only advantage I can see to the 450 is the fact its double the torque, but if its for changing wheels thats totally useless as the 200NM from the lower spec one like I have is more than any wheelnut should be tightened to anyway. In fact I used a 90NM restricted torque bar when using mine on wheels anyway to ensure it doesnt over tighten them.