I got the m-500...and i love it. The new r-500 is a little better system with realtime data, and data storage. My m-500 needs to have the laptop connected via wireless to capture data. However, there is still always a large digital display. I only got this unit last fall because i wanted a data logger. The system is worth its weight in gold. The LM-1 might be cheaper, but I love the look of the m-500, and when you start adding the data logging feature to the lm-1 it ends up being only a $40 difference.
I do believe that I will switch to this new r-500. It uses the same 02 sensor, o2 harness, data logging harness, software, so i'm hoping that I can just buy the display and save a tone of cash.
Like i said, I love my m-500 now, its always hooked up in the car and I look at this gauge now more than I look at my speedo. The ability to know just how your engine is working is great. The data logging feature is priceless at the track, and it has saved my arse a few times from meltdown. I log mph, rpm, wideband, ACT, MAF, and TPS....so tuning is a snap.
All the features that I wished the m-500 had at the time i got mine are built into the new unit. For example, i was under the impression that the unit would have on-board logging, but in order to log you need to run a laptop, not that bad. Also the wideband signal had to be fed into the data logging harness and was not automatically included. Like I said, it was just a few random things that don't bother me.
You can get the M-300 for around $330...close to the price of the lm-1 and its more of a permanant display and a smaller unit. Thats the main reason i chose PLX.
Oh and the wireless range with a good up to date PC is about 15 feet. I run it in the pass seat and never have a problem with signal loss.