Quote from theMarc »Rager is occasionally played in Commander. And only in decks that can reuse and abuse its etb, but don't have access to blue creatures with better draw etbs. Any deck that has room for Tithebearer Giant would rather just run Phyrexian Gargantua.Quote from krishnath »The opportunist is for Orzhov taxing decks, as a potential finisher. The Giant is overcosted for most formats, but has a decent body for its cost, and works as a bigger Phyrexian Rager, a card that is played a lot in Commander. Casting Cost and activated abilities with high costs are not really an issue in the format.
Vampire Opportunist, meanwhile, isn't significantly better than Bloodrite Invoker, and all of the invokers see little, if any play. According to EDHRec, all twelve invokers collectively see less play than Maze's End.
Just wanted to echo the above sentiments that these are way too slow for EDH. Phyrexian Rager saw some play maybe a decade ago when EDH decks were much less optimized and our choices for value ETB's on creatures were much narrower. No offense to Krishnath at all, but we EDH enthusiasts groan every time someone mentions a 6cmc fringe playable common as "Commander fodder".
As for the cards themselves, I think they're all solid for limited. The vampire is ridiculously expensive, but in a late game stalemate it could be a great way to slowly chip the game in your favor. The Knight will be great at holding off aggressive decks and the giant is a big body with card draw attached, nothing unplayable there. The rogue is a bit meh, but I could see him doing work in an aggro deck for limited.