I have TSA Pre-Check and CLEAR memberships. At LaGuardia's terminal B, there is no CLEAR. The TSA Pre-Check line was really long a few days ago (I estimated 20 minutes), so I walked over to the B-Fast lane (which is regular security, not TSA Pre-Check) and had paid for a B-Fast pass.

B-Fast is a total waste of money if you have TSA Pre-Check.

First, the airport agent at the head of B-Fast line said that she had to log in on her device to let me use B-Fast. I sat there for a few minutes while she worked to log in. Finally, after several minutes, she did.
Second, the B-Fast line had about 15 people in it, so it wasn't nearly as fast as CLEAR would be.
Third, the TSA agents let people from the regular (non-Pre-Check) line repeatedly go to the ID check stations but refused to let anyone from the B-Fast line go. The TSA agents also let dozens of wheelchair passengers go, too, but still refused to let anyone from the B-Fast line go. Finally they started letting people from the B-Fast line go.

Using B-Fast took about 15 minutes from the time that I entered the B-Fast line until I got past the X-ray conveyor belts. That was only marginally faster than a very long TSA Pre-Check line.

Bring CLEAR to LGA Terminal B and get rid of this B-Fast ripoff!