Force BS - Is it still worth it?

I believe semi-carry, he still managed to get a ton of kills though.

I'd get it, there's really no problems with it, offers utility and you'll get your damage from Bloodrage for the moment.

You need Blademail to make BS viable.

I didn't watch that BS competitive match, but I'm sure the enemy team had something like a Gyrocopter that is not weak at all when standing still ( Rocket Barrage still works), otherwise the Blade Mail is outclassed by other common items. I think that Bloodseeker should be built as a utility Hero; as I said before, I find Phase Boots and Urn of Shadows enough for his core, then anything that gives survivability is fine: Blade Mail, Drum of Endurance and even a Sange (which can be built into a Heaven's Halberd later), depending on the enemy team composition, are good choices. Just like when playing Razor, Bristleback or Elder Titan, survivability is better than damage since BS also has a damage steroid past level ~14.

I don't play this Hero that much, but I've tested different builds in bot matches and watched vodeos/read opinions of some competitive and semi-competitive players. Just try out those utility items and think about them; about the Force Staff, as I said before, I still consider it fairly useful past level 11 as it gives a safe escape mechanism and some needed mana.