The shard committee is designed to have a minimal number of required members so that the chance of getting a majority of malicious nodes in a shard is so small. I happened to write an article before, and Gusti Albrecht summarized it with a formula.
In the formula, we assume global 1/3 malicious nodes(N/M = 1/3 in your notation). We analyze the probability of ...
there are no drawbacks, just a bit more time taking... get an old laptop, run a light node, use it how you want. You have mempool & tx query via other nodes.
I run nodes for all my clients in the cloud...even have ones that haven't been restarted in 2 years so it's pretty solid