No hassle at all, when I stayed at Holiday Hotel they booked everything through Tropic Air for us and everything was covered. This included all flights, transportation from the airport in Flores to the Tikal site, a knowledgeable guide, and a prepared lunch.
The only problem you're likely to have with full day trip from SI to Tikal is that you'll wish you had an extra day (or days) to spend touring the magnificent site.
Lamanai is also an excellent site, it is pretty large although not on the same scale as Tikal. The trip along the New River to the Lamanai site is very enjoyable, we saw baby crocodiles, a couple of monkeys and a wide variety of bird species.