Roger,
I recently got an Interstate -- I think the model is MTP-24F (I'm away from the car right now) -- and am quite happy with it. IMO, it is much better than the Mercedes battery I had before. The car cranks faster, starts better, and even the clock seems a bit more accurate. The Interstate cost less than half the price of a new Mercedes battery, even with a 26% discount.
BTW, the Mercedes battery in my 230SL lasted about 6 1/2 years, which I guess is reasonable. The original Mercedes battery in my ML320 lasted just over 7 years. But the Diehard in my BMW 3.0CS is over nine years old, and is still working fine.
Chris