This is a comparison I put together half a decade ago. My findings now are the same as then. The Williams Sound Mic 090 is a little known secret- a lav mic that performs similarly to much higher end and expensive mics at a fraction of the cost. In fact as I post this now- it's dropped in price to $49.
It lacks a threaded locking pin and the physical design is a little bulky but the sound it delivers is excellent. Additionally through the past 10 years I've had my Sanken COS-11Ds needing cable repairs ever 4-5 years (despite being very careful with how I spool the cable and store the mics) meanwhile these Williams Sound Mics have never failed me.
In this video I compare the: Sanken COS-11D Countryman B3 Tram TR-50 Senal OML-2 Williams Sound Mic 090
All mic are connected to individual Tascam DR-10C audio recorder using the exact same settings (Mic Sensitivity: High, Auto Level: Off, Low Cut: Off, Limiter: On)
The results are shocking. Both the $234 Tram TR-50 sounds quite a bit like the less expensive $189 Countryman B3. More surprisingly is how similar the $75 Williams Sound Mic 090 sounds like the $379 Sanken COS-11D in both tonal response and sensitivity.