@Guillaume_1978 

Are you using sim cards for Internet only or normal sim cards (voice, sms, Internet)?

I have checked on Amazon and many people are very happy with these devices, working without problems. 

@Ermu my wind tre sim is only data

@Fabieuz 

This is what you mean about provider policy?

Prior to October 2018, Three (UK) had a number of different restrictions on tethering and personal hotspot. For instance, Essential Pay Monthly contracts that were sold between July 2016 and September 2018 didn’t allow the use of tethering.  

@Guillaume_1978 I know that some operator disconnect periodically all connected clients to avoid dropping prepaid sim's traffic from all pending connections

@Fabieuz I understand what you mean. I have a business SIM from Vodafone, all in, no restriction.   It is faster than Three (thanks to Vodafone's 4G+ / LTE network quality) but it also gets disconnected regularly.

@Ermu Well, on amazon, there are also many complaints about disconnections and need to reboot...

@Guillaume_1978 

I have MR200 v3, the one without LTE antennas and is working without disconnection. On MR200 have about 15 - 20 Mbps but on same location with cat 6 device is increasing to 75 Mbps. landed here thinking for an upgrade to MR600, but I'll wait. In Germany the MR600 is available only on Amazon.

@Guillaume_1978 BTW It's very strange that disconnections happen every 4 hours exactly 

@Fabieuz Oh interesting. On my side, disconnections are quite random.

@Guillaume_1978 what is the minimum value of time between two disconnections? Minutes? Hours?