I'm sorry to hear that you had issues with our devices!
Indeed, RUTX50 uses the same modem as TRB500, however, the architectures of the devices themselves are quite different.
Could you try enabling the "Software flow offloading" setting found in the Network → Firewall → General Settings and re-run the speed test? Try using a few different speed test servers, as some of them could be loaded and not provide accurate results.
Also, make sure that all of the antennas are screwed in properly and the device is placed in an open environment with a good signal to the cell tower.
I'd like you to provide me with the troubleshoot file from the RUTX during normal operation. Troubleshoot files can be generated by navigating to System → Administration → Troubleshoot and can be attached to the original post. It will only be visible to Teltonika moderators.