I'm really excited to try out the Kris Swordsman! While they do have a chance do be worse than a regular Swordsman, a 6/8 chance to be potentially quite a bit more powerful seems worth it to me. Here's my evaluation of all the unique promotions of the Kris Swordsman, in order from most to least powerful:
1) Restless: Indisputably the best of the of the random promotions. Not only do you get a free Blitz promotion, you also get +1 movement, which essentially makes them like Mechanized Infantry (with the Blitz promotion) in the Classical Era! This promotion also makes me wonder: If you have two different promotion that gives a unit extra attacks (like Restless and Blitz for the Kris Swordsman), and you have enough movement points that you could conceivably attack more than two times, do those promotions "stack", and enable you to attack more than twice?
2) Heroism: An effectively free Great General is nothing to sneeze at, and if you have an actual Great General stationed under this unit, I believe it makes you almost effectively get the first half of China's UA. Now if that isn't crazy, I don't know what is! The only problem with this promotion is that it does nothing for the unit itself with it.
3) Invulnerability: As the name implies, this makes the unit into the perfect tank! They are much stronger in defence, and the promotion makes the Kris Swordsman heal faster than an Immortal! One nice side effect of this promotion is that it makes the unit more likely to survive to get more promotions and become even stronger.
4) Recruitment: Getting the main advantage of both the Jaguar Warrior and Janissary, but stronger, seems like a pretty good deal to me! The problem with this promotion is that it doesn't make the Kris Swordsman more likely to kill an enemy, but then again, making it more likely to survive tends to make the unit stronger in the long run.
5) Ambition: +50% Combat strength bonus on the attack is huge! The Kris Swordsman becomes as strong as its upgrade, the Longswordman, on the offence! Now, it does have an explicit downside, in that the unit is -20% weaker on the defence, but I think the upside makes up for the downside, even if this promotion makes the unit more unlikely to survive in the long run. Besides, I like this promotion much better than the next promotion, which is...
6) Sneak Attack: +50% bonus from the flank attack bonus! And since the flank attack bonus is at +10%, that translates to... +5%... This promotion is extremely underwhelming in what it does, and like this much less than Ambition because, even though Ambition has an explicit downside and this is technically all upside, the effect is so small that I prefer Ambition's massive bonus on the attack.
7) Enemy Blade: The first of the all negative promotions, I nonetheless prefer Enemy Blade to Evil Spirits because, even though this makes it almost impossible to go and try to conquer an enemy city with this unit, it is still decent on the defence, within your own borders.
8) Evil Spirits: The worst of the promotions one could get, and a pretty harsh penalty to the unit, that hinders it in all it does, unlike Enemy Blade. -10% effectivenes on the attack is not ideal, to say the least, and -30% (!) on the defence ensures that the unit will probably not survive long. Honestly, one would probably best be served by just disbanding a unit that gains this "promotion".
So, in review, I definitely think that the Kris Swordsman will turn out to be my favourite of the Brave New World Unique Units, especially since I like games of chance. One could argue that its unreliability, and the fact that one doesn't know which bonus (or penalty) one can get with a given unit makes it worse than the base Swordsman, but I think the unit brings an important element of excitement, and, then again, there's only a 2/8 chance of the Kris Swordsman getting an entirely bad promotion, so I think the gamble is definitely worth it, especially considering that, if you get lucky, the Kris Swordsman is potentially much more powerful than any other Unique Unit.