I use the 4 channel Pico. It's a very good piece of equipment.
I find the big drawback is the fact that it's PC based. It's a real drag to set up just for some quick measurements.
Until mine died, I'd mostly use the PMS100 for convenience.
I couldn't even think how to work in a mobile situation, I suppose if you start young enough.
For mobile use in the great outdoors I'd be tempted to go for something self-contained like a Vantage or similar.