We have switched most of our blocks to Garhauer and have been very pleased with them. The Defender prices on Lewmar Synchro blocks are quite good - they are almost down to the cost of the Garhauers. But note that the Garhauer equipment really compares to the Lewmar Racing blocks, not the Synchro, and for those blocks Garhauer appears to keep its price advantage.
The spinnaker halyard turning block was one of our last Lewmar Ocean 2 blocks and I had not replaced it due to infrequent use. It failed this summer, sending the shive over our heads like a missile. I noted that it was the pin weld that failed, and the block opened up like a clamshell. A nice feature of the Garhauer and the Lewmar Racing blocks is, a design with no pin.
If you haven't handled the Garhauer in person, my advice would be to buy one of each, put them side-by-side, and I think the Garhauer answer will be obvious. Return whichever you don't like.