The difference between the NX-17/40 is that the NX-33 is that the latter uses fabric from the Certus series of chips. So the NX-33 has only one PLL, no DDR support and no Data Q Strobe (DQS). DQS is output by a memory chip, signaling it to register what is on the bus. NX-33 also exposes a 5 Gbit/s SerDes channel.  The $250 NX-33 tinyCLUNX developer kit is recommended. For applications requiring more bandwidth one has to use an FPGA not supported by the open source Yosys synthesis and Nextpnr placement tools.