Primos Jackpot slate (not glass) is easy to master and a good value. Box calls are also easy enough--Joe mentions maintenance, which is true, unless you get a wet weather box, which are no maintenance, but only last a few years (depending on how much you use them) and then you have to buy a new one. I like mouth calls, and, they are a little difficult to get the hang of, but once you do, you can become (reasonably) proficient with them fast.

"I do a lot of predator calling, so I'm assuming that turkey calling will be similar in that you'll use one sound to bring them to the field, then have another sound ready to coax them further into range?"
I don't know much about predator calling, but I assume your doing call that have a predator coming in looking for a meal. With a turkey, its all about mating, so they are want to come in. Often, rather than trying to coax a tom in the last little bit, it makes more sense to shut down and make him come looking for you (I guess I'm thinking spring turkey here when I talk about mating, so if you are talking fall, the previous may not be that relevant--also, if you are talking about spring, don't forget locator calls). Anyways, good luck.