I signed up with Allstate when I switched from State Farm. The first six months I saved around $300. Next renewal I only saved $13 and change. I'll give it one more go round and see what happens. If I don't see bigger savings I'm going to drop it.
Allstate and State Farm "trackers" work differently.
In addition to tracking how many miles you drive State Farm looks at hard acceleration, hard braking, cellphone use, and whether you drive more than 10 mph over the speed limit as defined by Google maps.
Allstate doesn't care about acceleration or the speed limit. In addition to miles driven, they track whether you drive at 80 mph or above regardless of speed limit (there are highways in Texas with 80 mph speed limits and one or two toll roads with 85, but Allstate doesn't care), hard braking, cellphone usage, and late night driving which is supposedly more dangerous.
Edited to add that while both say you can save up to 30%, State Farm guarantees savings of at least 10% whereas Allstate does not.