Ive got a Spot. I'd say its ok. Pretty basic but I guess could help save your life someday. Can take a while to send a message and a few can go missing. That said Ive never really used it in anger since I acquired it.
I put it on my windowsill this morning in track mode to make sure it works ok. You can see the results at
SPOT Shared Page. No idea how #18 ended up over there.
If you have mode S then I understand the guys at
www.aircraftbooking.co.uk have developed a tracking feature as a no cost option for their online booking system.
Also its worth mentioning that the SPOT will let others track your whereabouts online. And summon help if you get into poo. However if all you want to do is review your own track once on the ground then a GPS is probably a better option and certainly more accurate. I have Memorymap and Garmin 296, both will log your track and let you download it to your PC.