There are some technical objections to the design of flakes, but the controversy in the community is primarily social imo.

The reading I'd recommend as someone sympathetic to both 'sides' isn't really a technical comparison, but this: https://grahamc.com/blog/flakes-are-an-obviously-good-thing

As far as technical pros and cons, it's worth looking at colemickens' PoC demonstrating that in principle, you can use Nix to generate literally identical output with and without flakes: https://github.com/colemickens/nixos-flake-example

> Both approaches

it's also worth noting that prior to flakes, there was no single alternative approach to the main problems flakes aims to solve. There were (and are) a whole bunch of competing and bespoke practices for pinning nixpkgs and other Nix sources. You can take a look at niv and nix-thunk to get a sense of them if you want