Strangely enough, when I went to Virtualland arcade at Bugis the last time at the beginning of this month, I was surprised that certain IIDX Tricoro songs are in Jubeat Saucer. That included the songs from Legend Cross and Omega Attack events. Basically, that event was the crossover of Beatmania IIDX 20 Tricoro and Jubeat Saucer where the songs are brought out to each other. I guess that songs from Tricoro are somewhat less difficult to play in Jubeat Saucer but the songs from Jubeat Saucer can be difficult the other way round. Other features of that event involve delivering sweets to Tran so you have to keep playing either of two games to gain additional stuffs so that you can give them to her to increase her happiness. This is Project Diva F's Diva Room on steroids where her happiness level decreases over time so playing everyday is an insane task for arcade gamers like me and besides, every run costs money so what's the point of fulfilling this event.
Also, to unlock the song, Confiserie, you have to unlock all the event songs from both games so that you can unlock it in both games. It can be a tedious task in case you find IIDX seriously hard like I've been finding it hard to start off.
God, the Bistro Saucer thing, I bet it takes me forever to unlock other songs I know and want to play. Oh, the event is bound to be over by the time we reach April I think. I don't know if the songs from this event will be playable in Jubeat Plus. At least, that is the easiest way to get them played in the first place that you can save money that way and that can be what Jubeat Plus can drive you, a mobile arcade gaming through App Store, not those money consuming events that take time to complete so that you can unlock the songs. However, if the event songs are likely to be unavailable in Jubeat Plus like Konami has no plans whatsoever, I'm sure that you have no choice but to play those two games to get those songs playable.