I've run a 4-node baseline off trunk without +UseTLAB and here is the average result:

stress -n 2000000 -o read -i 1
Averages from the middle 80% of values:
interval_op_rate : 21918
interval_key_rate : 21918
latency median : 0.9
latency 95th percentile : 2.7
latency 99.9th percentile : 40.2
Total operation time : 00:01:42
END

With +UseTLAB I do indeed get better results:

Averages from the middle 80% of values:
interval_op_rate : 28352
interval_key_rate : 28352
latency median : 0.7
latency 95th percentile : 1.4
latency 99.9th percentile : 22.3
Total operation time : 00:01:21
END

Looking at interval_op_rate, that's ~30% increase in read performance. Interestingly, I see more variation in the interval_op_rate with UseTLAB - the first run I ran was much closer to the baseline at 23065. I never saw that much variation without UseTLAB, but I never did see a value that was below the baseline average, so I see it as a benefit to turn it on even though it's less consistent.

Write performance did not noticeably change.

Incidentally we've operated with this option enabled for a few months now and have observed reduced latency as well