Tim, I have no data on speed. The Nano may well slow things down but, at any point in time, I might be connected via Nano or direct to Mobley. Our primary need for more than Mobley's 5 connections is when we're at our town home in OH and we have 3 nearby grandkids staying over. Each of the kids can have 1 or 2 devices online at the same time. I'll pay more attention next time we're there, but it will be a while; My other half just had surgery with another to follow, so we decided we'd skip our winter sojourn this year, and hopefully return during school summer recess.
Separately, while at our place in WY we have local cable Internet (no ATT service) with a router in an outbuilding. The wireless connection to that router is hopeless, so I ran a 50 foot network cable to connect the router to the Nano in the coach, and all was well. Again, I don't recall if I took speed measurements or what the results were, but my wife and I were both streaming videos.
Here at our S&B primary residence, we have Comcast Cable internet, so no need for Mobley or Nano. FWIW I recently dropped T-mobile service after 12 or more years. They no longer provided any advantage over my other services, and ATT was half the monthly price.