Disclosure: I’m in Flexpool support, and I was the first person to use Flexfarmer on mainnet over a year ago.
I wrote about features and benefits of flexfarmer at the beginning of the year on my personal blog.
You need a synced node for plotnft operations (join/leave pool), wallet operations (if you don’t use a third party wallet), and to get the farmer secret key for Flexfarmer configuration (lets your Flexfarmer instance sign partials and blocks, does not give access to your wallet).
Once you have the plotnft created and joined, and the farmer secret key extracted, you no longer need the Chia Blockchain software running or the wallet synced, although a minimally-scientific survey I did last year showed that a lot of Flexfarmer users still run a full node (or more) to help secure the network and do full node functions when needed.
Upsides are very low memory usage, real reported space information (not just estimates based on 10 points per k32 plot per day), an easter egg in the log when you find a block, Prometheus and Discord hooks, naming your own workers (and changing names if you want), DOH and SNI features (for people in restrictive network environments), and automatic region failover between pool regions. It runs on any modern platform/OS with Golang (Raspberry Pi class machines, including 32bit, are popular, as are x86 x64 systems of course), and there’s easy implementation in Docker containers (including on Synology NAS).
Potential downsides include only working with Flexpool, not working with OG plots (if you still have them), needing one instance per plotnft (although it’s still usually under 100MB of RAM per instance), and not adding to the decentralization of the network (although as noted above, you can still run full nodes alongside Flexfarmer). Also, to add directories to your flexfarmer instance, you have to restart the client, which could mean up to ten seconds of downtime.
If you do run a full node and Flexfarmer, make sure you are not farming the same plot dirs in both or you’ll get weird stats and lots of stales.