Andy is always the voice of reason....and in my opinion, spot on with this issue. I have spent a fair amount of cash on a number of things that I seldom or never use. It just seems to be the way this hobby/occupation works. TBC, IMHO is great for lots of things and is undoubtedly more accurate....having said that, as previously stated takes longer, and with two barrell pens seems maybe, a little "disjointed". I do however TBC a fair amount. I have some Johnny CNC bushing and they are second to none!!! I like to turn a lot of different pen types, so a lot of the bushings are not readily available in TBC, and by comparison TBC bushings are expensive. So I have used a 60 degree drill on the ends of some "off the rack" bushings to allow them to be used TBC.
For some reason I just feel more comfortable on a mandrel, and I use a 8x1 adapter instead of a MT2 to hold the mandrel. If you don't keep that MT hole clean it can and will effect the way the mandrel sits. Further, I have thrown mandrels away over the last couple years. ( 3 or 4 maybe) They will bend and get damaged. I almost always have 4 or 5 kinds in my tool chest. Roll them on your table saw casting to see if they are flat, if there is some question...pitch it! (Do the same with your drill bits too)
I think you will find a lot of great turners on this site that swear by TBC, and their work is fantastic, but you need to do what you are comfortable with. There are many techniques for most any process, experiment to see what you like. ( Of course get your Mastercard ready)