To study, I used the ARRL Technician Class Study Book. It gives a good fundamental overview of what is being asked in the questions, so you can answer, knowing why you answered it that way.
To prepare for the tests, I used the flash cards and tests at https://hamstudy.org . The test layout on hamstudy.org is the exact layout that they used for testing. The testing with GLAARG is based upon the same backend. So, it looks exactly like what you see at hamstudy.org. You use a tablet to take the test, and all of the test results are immediately gathered. That is how they can send your results to the FCC so quickly. This electronic integration is why you do not have to wait for weeks to get your ticket.
There are some people who simply study the questions at hamstudy.org and pass the test. They say pass the test, then learn from experience to round out your knowledge. I prefer to learn the material first, then test. It just felt better that way. In computer networking, those kind of people were referred to as "Paper CCNAs" for just learning the answers, not the concepts.
One plus of the radio that the Papa Systems provides to the new licensees is that it can be easily modified to transmit on GMRS frequencies, also. One radio for both services. Not that I would encourage people to become scofflaws and perform such a dastardly deed.