Why I mostly phased out tallow soaps
This post is not a comment on the quality of tallow soaps. Tallow soaps are great. In fact, initially I bought tallow soaps exclusively. But over time, some quirks in my shaving routine led me to having a better experience with vegetable-based soaps.
The first quirk is that I shave with a scuttle and my tap water is pretty hot. Over time and extensive testing, I came to realize that animal fat HATES a hot scuttle. The heat seems to really cook the fat down to nothing (some soaps disappear altogether) whereas my veggie soaps have no trouble being heated up. Couldn't tell you why, but I can say I have tested this on at least 60 different soaps.
Secondly, unlike many, I am a big user of pre-shave oil (especially Stirling & AoS). I love the slickness and slather it on before all three passes. So, whatever fat slickness I am losing from not using tallow, I am making up for in oil fat. So, I came to realize that if I want a hot lather with lots of slickness, veggie soap + oil is the way to go for me.
Now, if I'm cold shaving on a hot day, I still have lots of Stirling, Dapper Dragon and Ballenclaugh tallow soaps waiting in the wings. Those are all great products.