E2 Testing Immunoassay vs LC/MS/MS

I’m a little over four years into TRT, and doing well. I have always had the immunoassay estradiol test and results are usually 20-24. I’ve been aware of the LC/MS/MS ultrasensitive test.

Recently, in part due to what I have read here, I asked for both and received these results:

immunoassay: 21 < OR = 39 pg/mL
LC/MS/MS: 23 < OR = 29 pg/mL

I understand that with the immunoassay, if the result is <15 it will not register, but since mine is not, given the above results, why would I want one test over the other or why would I insist on the ultrasensitive test?

Thanks for any insight.