Dave,
I have a newer Summit Systems SRT 1000 Timer, it works great and is pretty bomb proof in terms of the weather proof rubberized shell. Battery life is excellent too. Considering the price of about $500 for the non-wireless and about $900 for the wireless mode they're a great value.
I've used them mostly for backup timing in conjunction with the AMB Activ chip system. I've also rented the wireless models, they provide awesome range using the MaxStream (
http://www.maxstream.net) 900mhz OEM cards and the standalone radio modems at the central processing end.