When I started using pellets, I converted a large MRC media reactor and nothing but problems until I shelled a few hundred dollars out for the Reef Octopus pellet reactor.
If I had to do it all over again, I would look at the recirculating reactors because you can increase tumbling without effluent output. So in the case of my Reef Octopus, I have to use a bigger pump resulting in more flow output whereas all I really needed was a recirculating design like the Reef Dynamics reactor. The two recirculating reactors that I know of which is Reef Dynamics and Reef Octopus Churn are pretty pricey though.
I'm sure others will add to this post if they have had good experience with other less expensive pellet reactors.