I'm the one who asked the question in the other thread.
The Bad Seed and the Mantra Junior have almost the exact same profile at 113-80-104 (105 in the tail for the Mantra Jr). The longest you can get the Mantra JR is a 138, whereas the Bad seed comes in a 149.
I asked the question in the other thread, because while I was attracted to the Mantra Jr. for him, I thought a 138 was going to be too short to get more than 1 year out of (He skis 142 SL skis and 158 for GS).
I ended up going with a pair of Fischer Villian Pros in a 154 - mainly because they were available at my local shop. At 110-80-110, they are pretty similar in float to the Bad Seed - actually a little wider in average width. 154 Sounds long, but remember that twin tips are going to ski about 10cm shorter than stated length.