There seems to be quite a bit of confusion on this topic. Hopefully, I'll clarify the situation, rather than adding to the confusion.
The "regular" E2 test will give you a numerical result if your E2 is above the limit of sensitivity of the test. For example, my lab (Quest Diagnostics) gives me a specific number if my E2 is at or above 20 pg/mL. But if my E2 is less than 20, the result they give is simply "<20." That result is not very good because you don't know if your E2 is 0 or 19 or somewhere in between. OTOH, if your E2 test result comes in less than 20, the ultrasensitive assay will give you a specific number between 0 and 19.
But if your lab gives you a specific result of 20 or more, then the test that's been done is a good one and you can rely on it.
I actually prefer the "regular" E2 test because my E2 virtually never comes in less than 20 (it happened only once in about 50 blood tests over 5 or 6 years) and the results are available in about a day or 2, whereas the ultrasensitive test takes about a week to report out.