I've had my V20 for at least a couple years now and loving it. The performance is really good, though a recent google update was laggy at first. My one phone without a replaceable battery was, oddly, the LG G2 and swore I'd never do THAT again.
Don't see any reason to downgrade to newer phones made to be disposable if anything happens to them - i.e. run down battery, cracked screen.... They cost WAY too much to be disposable just because the battery runs down after a couple years. And pretty glass backs just make repairs nearly impossible, so not even a consideration.
I saw a foldable phone, the screen already showing signs of a crease - no thank you. Really, I have a laptop if I want a large screen or a TV at home.
Just replaced the V20 battery with a 4200mAh by AexPower off Amzn - it fits with the V20 back and lasts me all day+ most days. And it works perfectly with LG and Anker chargers. Having that extra life fitting inside the LG back means the Poetic case fits too. Really liked the iPossible battery, but the case was just too easy for the little ones to remove (they like the bubbles on the lock screen when they touch it, another cool LG feature).
Overall, the V20 doesn't miss a beat. The pics are great (I use the manual mode), call quality is great, and the Quad DAC sound is unbeatable. Bluetooth sound is okay (meaning BT not the phone), so I plug an aux cable from the V20 to the car for amazing. I have Sony & AKG phones and both sound great on the V20 (The car speakers and these phones are totally weak tea on my friend's s9 by comparison).
I much prefer the interface for the LG, vs Samsung, especially the manual controls for the camera & video. And the mics do just an incredible job of recording. When I first got it I was blown away at the detail captured and that they don't top out with loud concert sound.
As to buying NIB or used. I got mine in a panic through a nearby Phone Clinic. The G4 I was using died & I needed something immediately. They had a used V20 handy so they transferred everything and it didn't miss a beat. Ironically, I went to register it via LG and found it had never been used on any network - so new. And it only cost me $250. Been super happy since.
BTW, I hate phones with powerbuttons on the side as I would constantly press it with my thumb accidentally just holding them. So the power button on the back, well placed below the cameras, works perfect for me and having that also as the fingerprint scanner is a perfect combo.