I think the bundle (the one for 85 EUR) is not interesting for you because you don’t need the antenna nor the usb adapter. What you might want is the option “only EM06-E” and if the seller is actually legitimate and this is really the Quectel EM06-E then that should work fine in the Pocket Reform.
Pain.
I don’t have a good solution. I grabbed some random LTE antennas, similar to this one:
But I’m not 100% satisfied with the result. It works when I’m stationary but connections drop frequently when I’m in a moving vehicle like a train.
The hardest part is to find an antenna with the right connector. There are not many options with the MHF4 connector. Most antennas will come with a connector that visually looks like a larger version of MHF4, the MHF1 connector. Be careful that you don’t end up with the bigger connector.