Having a way to keep a big creature on the board for the low cost of holding a single land open is an essential part of most formats, and Tamiyo's Safekeeping is one of the best you could tuck away for when you're in a pinch
However, an ability like Sen Triplets makes it a prime target for your opponent's malice, making me think that you won't get to keep it in play as often as you think
This commander works with X spells, but that commander works with +1/+1 counters
Mainstays like Robin Hood get multiple cards, and Pete and Heihei can be found within, too
While the card not doing anything when you cast it is a shame, you only need one turn with this thing to completely transform your board state
With the current context in mind, this card will play an unfilled role