I've had a Block Rockit ever since they came out. I've used many types of threads including serger thread, embroidery thread, threads from Connecting Threads and it sews them all beautifully. The only thing is getting the tension correct. Yes for some types you may have to go to a larger or smaller needle depending on the size and type of thread but the machine should sew it once set up correctly.
Some machines just don't like a particular thread but that's pretty much in all brands of machines. So far I love my Block Rockit.
David