Just thought I'd wade in...
Having seen the Martha one in real life, I would definitely go for the popular EK success one that's been around a while.
The Martha one looks like it's open to human error and that it wouldn't be too difficult to end up with a duff cut that doesn't meet the original line. I've not really seen any rave reviews for the Martha one, but the original EK success one, not the circle scissor one, seems to still be top dog.
Plus you won't have trouble trying to source spare blades for the EK Success one since it's popularly stocked over here.
A few folks on our trip to Florida were tempted by the Martha one until they looked closer and it just didn't look like it would really do the job perfectly... her punches on the other hand were a huge hit!