I've scoured the forum looking for recent posts regarding BritRail passes. Most posts are years old. Do any travelers have more recent (2022-2023 travels) experiences using the passes? We're looking to take a total of 3 trips on 3 different days (London-York, York-Edinburgh, and Edinburgh-London), so we were thinking the 3 Day Flex pass would work best. Even though seat reservations are not required, is it still a good idea to make them? If so, what is the mechanism for making these reservations? What's the comfort level in Standard Class? Is it worth upgrading to First Class?
did you ask the Man in Seat 61 yet?
A few ideas for you. First. Take the time to price out the difference between your three trips with advance purchase and the BritRail passes. Then price the three journeys out as if you had purchased a "two together rail card" which provides a 1/3 off rail discount for most trips (a few restrictions exist). This will give you a good idea of what the savings are for the various options. There really isn't another way to tell if the Rail-Pass is a good option or not unless you absolutely need the flexibility. If you are wondering about reservations, that leads me to believe flexibility isn't a big issue for you.
Standard class is usually just fine for most people. Some people opt for First Class because they are trying to reduce the number of other people in the carriage, and most people aren't going to pay for First Class.
About seat reservations on LNER (the most likely company for these trips)- if you just book individual tickets for these 3 trips they are included with your ticket at the time of purchase (you choose your seat).
If you decide to use Brit-rail, then seat reservations are highly recommended. Otherwise you may not get a seat. You reserve your seats on LNER through this web-page.
https://www.lner.co.uk/travel-information/make-a-reservation/
If you use Brit-rail and travel on Grand Central trains between London and York see this web page on how to reserve seats on their trains (or book in person at a staffed station)-
https://www.grandcentralrail.com/help/faqs/tickets-and-travel-information/how-do-i-reserve-seat
If you use Brit-rail and travel on Trans-Pennine express between York and Edinburgh make a seat reservation at any staffed station in the UK (less necessary on their trains which usually have more room).
The same applies to Lumo trains, if you choose to use them between Edinburgh and London.
On all operators if you just board without a reservation there are electronic displays above each seat which clearly show which seats are un-reserved. Green for un-reserved and red for reserved.