Basicly, he's like the prototype juggernaut for the Juggernaut Reworks. He deals tons of damage while being tanky; but, he has tons of cc, so I don't think he's much of a Juggernaut.
Randuins is good if you're against a crit heavy team. I personally like Dead Man's because it lets you catch up to people faster. That, combined with the slow, you have a good chance of being able to stun/devour that person. And what's scarier than a Tahm running at you with 500 MS?
Frozen Heart is a suboptimal buy for Tahm Kench. The CDR is good, but Tahm mostly focuses on building Health, which is why most of my items have a lot of health. Frozen Heart is good for some situations, like if you're going against a Vayne ADC and Gnar Top; otherwise, I wouldn't buy it.
The boots can be swapped out depending on the situation. I personally like Ionian because then you get to spam your Tongue Lash, Devourer more people, and have more global presence with your ult. Mercury Treads come a close second if they have a lot of AP/CC champions. I don't really think Tabi is very good, unless the other team is mostly AA reliant; in that case, Frozen Heart and Randuins can easily fill the gap. Another boot to consider is Boots of Swiftness if you aren't getting Dead Man's, because then you'll be able to catch up to them, especially if the other team is kite-oriented.