Yeah, I'm a wee bit confused by that. Assuming the LA6M is indeed twice as fast as the LA3M, and not a larger factor, then...
GRIDSEED 3+ MH/S ASIC SCRYPT & SHA MINER: $2,285
x2 = $4,570
GRIDSEED 6+ MH/S ASIC SCRYPT & SHA MINER: $4,565
For $5 more you get redundancy and better resale value, at the cost of needing an additional power supply, port, space, etc.
But even that's not so bad since they have a complete package:
GRIDSEED 3+ MH/S SCRYPT & SHA MINER (Including PSU & Accessories): $2,425
x2 = $4,850
GRIDSEED 6+ MH/S SCRYPT & SHA MINER (Including PSU & Accessories): $4,835
Not seeing great incentive to get the LA6M instead of 2xLA3M. Must be missing something obvious - skewed shipping costs?