Lets compare some things

Keep in mind that Smoke Flash is unlike the single-target Placate in Stalker primaries in that it does NOT put you into a Hidden state. i.e. You will not get an automatic critical after using Smoke Flash. It merely placates foes which are hit by the smoke so that they stop attacking you for a short duration. In that sense it is something like an AoE sleep while solo and a rather unfriendly "go attack my friends" power on teams.

Not that Stalkers are meant to be friendly, mind.

It's got some active defenses to supplement its passives if that's what you mean. So it will seem more active than, say, Super Reflexes. But really, the only thing that will slow you down with ANY secondary is having to recover from battle. Ninjitsu, particularly paired with Ninja Blade and some IOing will have no trouble keeping you going... until you die instantly from a lucky one-two shot from a purple boss or something, but such is being a defense-based Stalker.

Quite well. Ninja Blade's Divine Avalanche will keep you safe in melee and being in the thick of melee is where you can really carve up your enemies with those short-range cones. The knock-up and down in Soaring Dragon and Golden Dragonfly really give you an in-control feel to a fight. It's great to slide up to a boss who is going after a teammate and dump him on his backside with SD then bring GD down on his head while he's trying to get up. The only thing that will really disappoint with Ninja Blade is the lethal damage type.

It's a very scrappy combo though. Divine Avalanche means less need to IO for melee defense and thus more room for other bonuses like recharge or damage. It also means you can put yourself well *above* the melee defense soft-cap, which is a life-saver in places like Cimerora where there are crushing defense debuffs, mainly from enemy melee attacks. And Ninjitsu does not have nearly the defense debuff resistance of EA or Super Reflexes.

Not only that, but it actually BREAKS hide, so if you - like me - have any notion of using it proactively against high perception targets like Rikti Drones, don't. The entire spawn may well be placated, but you won't get a critical.

Before you take it, I highly recommend getting the temporary power recipe of the same name and trying it out - I believe it does the same thing.

Oh, and to pretty much everything else Zem said (and including the above, for that matter): QFT