A few rounds with Mengsk talents, my 2 cents worth:
Toxic Tyrant
For those who like using mass ESOs, this one provides plenty of help.
Mandate generation with Troopers manning ESOs is significant, equal to that of Troopers standing under Witnesses. On Rifts to Korhal, I was able to hit a total rate of 360 with 25 ESOs fully manned. This also opens up spamming bunker drops. By comparison on live servers, the most you get is just 120, all of it from the workers at bases.
If the ESOs are all unloaded, Mandate generation drops like a rock in a swimming pool. Witnesses in Patriot Mode above the manned ESOs does nothing.
Spamming Contaminated Strike is kind of nice once you have a critical mass of ESOs.
Principal Proletariat
Not yet figured this one out but it seems to be for those who prefer Royal Guard Mandate generation and/or RG experience over Starting Mandate.
Looks to be a suitable for those who only use a handful of Royal Guard units or want a way to level them up quickly. Battlecruisers may find this particularly useful.
Merchant of Death
This one appears to be for those who are indifferent to expendable units or don’t bother with Intercessor healing.
When Troopers with upgraded weapons die they set off a miniature mushroom cloud that causes considerable damage. Not sure how much but it seems more than enough to wipe out Zealots in one hit. They also hit air units; in one game, Oracles were destroyed after flying directly above several explosions.
For another game, I suited up a group of Troopers all with weapons and ran them through a standing force of Protoss. Much of the Protoss got wiped by what looked like firecrackers with legs. Kinda cool but quite costly to pull off. Haven’t yet tried out camping upgraded Troopers on spawn points but I imagine the result would be hilarious.
Lack of Intercessor means no Marauder healing and no flying Siege Tanks; Troopers can convert to workers and repair each other if they need it.
For me, this one would be used out of boredom more than anything else.