For me this blade is a must since he can be good to form various combos. The secret bosses like 14 and glaive can be discouraging, but if you realize that you don't need to kill it within 1 hour then your burden could be put at ease.
Once spawn the 10M boss just damage it as much as you feel like contributing and send the distress signal to ask if any of your friends wanna do damage. Keep track on it if your friends almost kill it then you should take a chance to go at least silver for 1M damage or gold for 3M damage.
I'll tell you how we handled our secret boss, we set up a chatroom on facebook and try to add bout friends in riderbout so we can give alert and ask for helps in time of need on the very phone device you are using to play bout.
If your friend list has a lot of people who don't feel like participating much then you can kiss these bosses and exclusive cards dropped from secret bosses e.g. SR 14 SR Glaive SR Blade King Form and EX RSF goodbye since nobody is going to help you kill it for sure.