I have a Spottracker – I bought it primarily for the fact that it had the emergency callout facility that can be used where there is no mobile coverage and you can also send an ‘OK’ message to friends and relatives.
My overall assessment is that it’s definitely a v1 device in that it’s a bit clunky and there are things that could be improved – eg it could confirm when it has successfully sent a message, but I still think it was a useful investment as a piece of emergency kit. The positioning messages seemed pretty accurate. I found that it was best to set the device down in one place and give it 10 minutes or so to do it’s job. I would ask clients to use the check-in facility at meal breaks and in the evenings.
I don’t know whether you were planning on using it as a tracking device with the ability to show your clients’ position at any given time. Someone did a review on backpackinglight.com when they criticised the fact that the tracking on the move seemed a bit hit and miss. Personally I think the emphasis of the review was completely wrong, as it’s primarily an emergency device, but in any event while there were some questions about the device as a tracking device, my general impression is that unless you want to keep constant tabs on clients all of time then it’s good enough. I’m not sure if there is anything better that will work without mobile coverage.