Mirei's second effect is perhaps her best, allowing you to play a reciprocal Angewomon or Ladydevimon from hand. However, do note that the only Digimon in this roster that has a [On Play] effect is the [ST10-05] Angewomon.
While she is by no means a bad card at all, she is 6 cost to play, and synergies with Flame Hellscythe. Also, since she is mainly played in Mastemon decks, 6 cost to pass the turn for Jogress gives you a lot of freedom for not needing to setup and to be able to promptly react to the opponent's board at any time (given you have [ST10-04] Tailmon's inheritable effect of course).
With Mirei Mikagura, you will need some setup by first investing 5 cost for this tamer which does almost nothing, then digivolve into Angewomon or Ladydevimon in order to trigger her effect to play the other. While this does relieves some reliance on [ST10-04] Tailmon, playing a 5 cost tamer in the BT-11 meta in turn-1 or turn-2 may put you within firing range of the likes of Blackwargreymon.