I have recently purchased a TP-Link Archer MR200
, and am very happy with it so far.
I have a thread on the forum about my experience here: http://forums.thinkbroadband.com/mobilebroadband/t/4...
I can't get any 4G signal indoors in my house on my Smartphone (a WileyFox Spark X) - although I usually get a 4G signal in one spot in our field around 50 metres from the house. I do get an occasional poor (slow) 3G signal on my phone. This is all on EE, which probably has the better 4G coverage in my area (although we're right on the edge of any 4G coverage, in a poor signal area generally). I may try a Vodafone SIM soon as well.
But the TP-Link Archer MR200 does pick up a 4G signal indoors, and in 1 or 2 selected locations it's a 1-bar signal, that usually gives me a downstream speed of 12 to 35Mbps (dependant on signal strength, weather, time of day, etc), and an upstream speed of 2 to 20 Mbps - even the lowest of these is much better than my ADSL link, which gives usually 2.5Mbps downstream & 0.3Mbps upstream.
I do also have this external antenna: Solwise Omni-Directional
(actually a Poynting antenna) - which does work, but I haven't yet had the chance to test or position it properly - waiting for some better weather first! But from brief tests so far, the built-in LTE antennae on the router have provided just as good a signal. They are external screw-in antenna.
I would imagine that the antenna for the MR200 have much better reception than a MiFi unit, and the MiFi's probably in turn have better reception than many smartphones. That's just my feeling though. Of course, with the MR200 (and most similar LTE routers) you have the extra option of fitting an outdoor directional or omni-directional antenna, so more options still.
One extra point: the MR200 allows you to "force" the router into 3G or 4G mode (or otherwise "Auto" mode to select the best signal), which is a bonus, as otherwise I rarely pick up a stable 4G connection - in 4G mode my 1-bar signal seems very stable & consistent.
I'm now just waiting for a good deal / offer to come round again on EE 64Gb/month Data SIMs (has been around £30 per month or just under before now). 4G is an excellent back-up for ADSL (or indeed any other connection, even FTTC/FTTP or Fixed Wireless), or as a "turbo boost" for a slower ADSL connection - but due to the low data caps generally available, I don't think it could replace an ADSL connection completely (as mine allows unlimited data downloads, I'd always want that as a fall-back option).