As has been said, the games have to support saving to backup RAM in order to work with any of the devices. Bonk 2 doesn't.
The boosters are all made for Core systems with no CDROM2 device. The Ten no Koe lets you store copies of what's in a booster/CDROM2 device. The MB 128 only works with MB128 games and the Save-kun is just, IIRC, Koei's copy of a MB128.
If you are playing a game on a HuCard, don't be afraid to just pause it and walk away, for weeks even. PCEs are tough. If you are playing from a CDROM2 system, just pop the door so that the CD will stop spinning and then treat it as a HuCard system. The music will be interrupted, but it will come back at the next load point.