I started designing Transmission line speakers in the mid '70's. They can be real good for the money. These days I use a ported cabinet design because you can get a better final performance curve.
Though not a speaker designer, this meets with my experience.
I had pair of Spendor D7 which uses a quasi-transmission line bottom firing port. The bass and sub-bass was so deep and effortless, a speaker with very special bass. It improves the efficiency of bass response and makes them easier to position.
No, I don't believe the Spendor D7 or D7.2 even qualify as "quasi-transmission line" (whatever that means). They are simply bottom ported.