Joe,
I recently replaced some 20 year old KLMs with M2s. In most ways, the M2 are BMWs and the KLMs are Yugos, though they did a good job. (I need to do a little refurbishing on the KLMs, and will probably have them for sale if I am satisfied with them.) If you get the longer versions of each M2, recommended, be prepared for poorly written documentation with some cut and past from the shorter versions which is simply wrong in one case, and very confusing in others. You can sort it out by phone easily enough, since M2 does not return e-mail or phone messages in my experience. Still, for drawings dated 2000 to be this seriously in error, and not updated, does not speak well for them.
There were also a few parts, sealing rings for the type F connectors, which were missing. However, because I also ordered the CP switches, which had extras, I had enough. Finally, on the 70 cm unit, there are some very tight bends at the connectors for the phasing and switching lines. These need very gentle installation, and some additional water proofing. There is more than enough length on the 2 meter version. I didn't take the same to work it all out, but if they had added a wavelength to a couple of lines, or perhaps .5 wavelength to several, the needed phasing would have been preserved, and there would be no strain on the connectors.
I checked everything I could think of on the ground, and found the SWR, and the change with polarization, much better than with the KLMs. When I got the 2 meter version up, purely as an accident because of the particular SWR meter I use, I found that there was a 1K ohm or so short between the rf and dc switching lines in the 2 meter unit. I ended up opening the switching unit, easy enough, and found two things. First, the dc lead to the switching relay was just barely touching one of the rf leads. It was easy to move the dc lead away, but the problem was highly visible, and should never have been sold that way. Second, there were a couple of places where the rf wiring was connected using solder bridges because the wires were poorly installed. Again, easily fixed, and totally unacceptable for a unit which lists for $201.
The overall impression is an outstanding design, with great attention to detail, spoiled by some mind boggling carelessness in execution of rather small but important things.
Once you get them up and debugged, they really work well. The KLMs had significant side lobes, and it is obvious that the M2s are quite a bit better from that standpoint, though I can't do AB measurements. While I never had any problems getting into AO-7, FO-29 or VO-52 with the KLMs, I have noticed that I need to back off on the TX power significantly more than before to have a socially acceptable signal strength. The same on AO-51 and the other FM birds. Of course, it is nice to be able to crank up the power when shooting through the trees, or when the bandits are on the AO-51 uplink. Now all I need to really test them are some P3 birds.
Alan WA4SCA