I've played quite a bit with the hotfix version of Tahm now. His lockdown is terrible now, but his pick and gank potential with a 3 second 70% slow is insane.
The one thing that I really don't get now is the fact that he now heals for 100% of gray hp that you don't use. His shield used to be the one bit of skill where if you don't shield you only regen about 30% of gray health, but if you shield properly you have the chance to "regen" 100% of it.
Now your two options when jungling or laning are: back off and regen 100% of gray health, or shield and potentially regen 0%. There is no more reward to shielding unless you're about to die, at which point you'll probably die even if you shield because Kench has no escapes.
Once you get a spirit visage, the risk/reward ratio is even worse. I just don't get why this change was made.