TRIM is a good thing to have, and is a "big deal" for certain usage or if you regularly write a lot of data (e.g. gigabytes) to the SSD. It's not a big deal for most users because most users are just surfing the net and using basic productivity apps where there's not much being written to the SSD and the files are relatively small.
Most users who dismiss TRIM don't understand how SSD's work and what TRIM does (and why it's not the same as Garbage Collection)... they're just going by their own experience based on their own usage (or repeating what others have said), and for many users, they won't notice, and the lack of TRIM doesn't affect performance in the short term.
The easy answer is not to worry about it. An external SSD without TRIM is still way better than a HDD, so whether TRIM is working or not, you're still better off with the SSD.