You should also have a look at the much better performing Septentrio Mosaic series of GNSS receiver boards. There are dev kits available for a dual antenna heading RTK receiver for around €750. And €645 for single antenna. Dizzyingly cheap compared to what this class of receivers cost just a few years back.

These support all GNSS constellations and signals and do a real 50 Hz PVT in RTK mode. And they even come with a built in, quite useful web interface.