Disclaimer : I'm the auther of one of those phone Apps Steve rejects.

I like Steve's answer but he is being a bit harsh on phones. They have there place. You can forget to turn on any logger (I've done it). Phone power is mostly an issue if you use it as a glide computer because the screen is on full brightness 100% of the flight. This is LESS of an issue if you are just logging and can turn the screen off. If batteries are an issue, this can be easily solved by an external battery pack or connection to ship power.

For somebody starting out I see phones as a good cheap way to get started. As with any technology they have limitations. Phones are unlikely to ever be "IGC-approved", which means you can't use them for FAI Badges. They can, however, be used for OLC (and Skylines) and post flight analysis.

My recommendation is while you are learning, start with a phone. Move to dedicated hardware when you know more and want more. Spend the money you save on more tows. :-)

PS. Simplistically, ADS-B is primarily a transmitter so other aircraft and air traffic control can see you. Gliders with FLARM and large jets will be able to see and avoid your glider. ADS-B doesn't log anything.

Alan