AP's, not extenders. It makes perfect sense as it's true in my personal testing. Just because my SH3 could give me a usable connection on the top floor doesn't mean I would use it. My SH3 is in modem mode with an i3-7100t/16GB/120GB SSD ex Datto box running Untangle (or at least it was till yesterday). Not a great idea to add wifi on it as it lives inside of a metal comms cabinet mounted in the corner of two solid walls under the stairs... obviously that wouldn't end well and you know my views on making poor hardware/location choices. I've got the S510 down to 16w under OWRT, pretty sure I can get it a little lower, but that's £1.85/m+VAT to run 'as is', hardly gong to break the bank.
I'm confused, the discussion taking place is orientated towards running 3rd party routers/distributions, they all have a learning curve and all require you to do some basic administration/maintenance and are generally useful to people who want to do things the SH range can't. That may be VLAN's, WAN failover/load balancing, PBR, hardware accelerated VPN, QoS, and UTM functions or on-router services (docker for example). You seem to want managed updates, plug and play and little or no learning curve with simplicity and QoS. Other than the latter, they're generally ISP supplied router traits. Personally I wouldn't want an unplanned update taking down a live system at an innopertune moment, but that's just me. Any router can be misconfigured.
If you read Dave's earlier posts in this thread, it's clear he's not in the UK.
While it's flattering to be included in such company, I spend my time learning what I need to, that's where the fun is in networking. Again this really sounds like you want an ISP supplied/maintained router. You've had suggestions about hardware, even suggested some yourself, but your response suggests you have no interest in running a dedicated 'piece of hardware' (isn't that exactly what a router is?) or doing any form of set-up/maintaining/config which puts you into ISP supplied kit territory. Rather than focus on why you don't want/aren't able to devote time to learning - no judgement - why don't you try and focus on what you do want and what budget you want to allocate?
Most 3rd party routers will essentially be secure by default and close to plug & play, but things like firmware upgrades and configuring forwarding rules, policy based routing, VLAN's and Q0S generally need some level of user interaction as will any firmware updates, it's a trade off.
Hopefully later tonight i'll get to do some playing/testing and catch up on the wealth of information already posted above