well maybe some orb changers have some use but I got mystic flame knight who turns blue into red which is bad cuz I need blue for my haku, the blue ninja turns dark into blue which is bad cuz I need dark... you get the picture.
Even if there isn't a conflict, the number of times you need that one colour to complete the 3 combo is quite rare, and doing it just for added damage isn't that significant since you have a colour split and you'll really only have 1 or 2 creatures of that colour most likely. My persephone would be pretty good with my haku for orb changing I guess but I don't like gobbling hearts if I don't have to, and her base stats aren't impressive either.
And I do have a siren, I rarely use her though because I find I don't need a healer that often. Most of the time I can get by with echnida's delay. I'll heal up in that timeframe. That and I can't skill her up... actually I wanted to post that.. I just fed 12 marine gobbers to my siren.. 12.. still no skill up, and yes, it's x2 skillup.. ASFDJKLASKFJ. and yes, I've fed alot more than 12 on previous x2 events.. WHYYYY. Whoever said 60 echnida's guarantee's a maxed out echnida has hax luck imo. I don't even think 6-effing-hundred is enough to max my effing siren.
However I also got really really lucky... I opened 10 pal eggs and got: 1 super gold dragon, 1 super black dragon, 1 king red dragon, 1 king red dragon, AND an effing green golem (didn't suika or someone desperately want a green golem? I got one from a PAL egg sucker! hahaha =P)