I wish this video came out a couple weeks ago. I spent far too long trying to figure out how all the pieces come together, realizing I chose the wrong google apps package, twice, etc. Some notes: The Pocophone has unusually limited frequency band support. Compare with local carriers and see if you have adequate coverage.**
You probably won't find the (128GB) Poco at $300. I got mine at eGlobal Central for $350 USD, with free shipping (I'm Canadian btw). You can get it something like $20 cheaper at AliExpress; but then you leave yourself open to waiting like a month for the thing to ship (common complaint apparently), and possible duty charges. There's more information about resellers (and more) on the Xiaomi subreddit wiki. EDIT: Whoops. Yes it is $300 actually! I forgot I got the more expensive 128GB version.
Check the Xiaomi subreddit for information on resellers so you can get the best deal. I definitely saved money compared to the Amazon.ca price.
The main problem with MIUI is that it aggressively shuts down apps running in the background. There's an option to make it somewhat less aggressive, but it doesn't change as much as you'd like.
After that, it's mostly just little annoying things and bafflingly bad design decisions. For example, MIUI 10 by default interrupts your audio, for a whole second, every time you come in and out of range of available wifi. Terrible.
Really, though, it's not all that bad; but LineageOS is still far better, once you manage to set it up. Getting that down, the phone completely ceases to feel cheap or annoying in any way.
Wait, actually the phone is pretty gosh darned slippery without a case (Linus' "Kevlar" version isn't the normal one you'll be buying). I don't know if this is common for phones (my last was a Nexus 5). Mine came with a perfectly serviceable thin case though; so no real problem.
MIUI's gestures are actually a great feature which LineageOS lacks; but you can get perfectly excellent and customizable gesture support with an app like 'Fluid Navigation Gestures'. (Needs root to disable the nav buttons though, and occasionally the buttons come back in some apps.) ** I can't say much else on this, as I don't bother with phone plans, opting instead to use wifi -- via voip.ms (with apps 'Bria Mobile' and 'voip.ms SMS') which gives you a phone number from whatever region you like to make/receive calls, and supports sms. Costs about a couple bucks a month. Even less if you don't use Bria. Like the Poco though you really do need some guidance to set it up (thankfully there's a wiki). Maybe Linus should do a video on this kind of ultra-cheap setup, perfect for nerdy folks who hardly leave home anyways.