While LGPL and MPL are similar, there are differences and they should not be lumped together.
The biggest difference is that MPL allows static linking while LGPL does not. While in the past this wasn't a big deal, it is important for iOS development since you cannot dynamically link to libraries in iOS apps.
Well I doubt it'll be any lower than the industry standard of 2.9% + $0.30 for < $3k/month. If it is, that would be pretty disruptive.
What will be more interesting is if they can match both Amazon and PayPal's microtransaction rate of 5% + $0.05 for products under $10 (Amazon) to $12 (PayPal).
On the surface they are more expensive than PayPal (2.9% + $0.30) Fees.
The fees for Stripe are 5% + $0.30.
However when you take a deeper look you see that things are not so simple.
Compared to PayPal's free product, you are not forced to leave your website and go to a 3rd party site to complete the transaction.
Compared to PayPal's Web Payments Pro product, you don't have the $30 monthly fee.
Also this doesn't even taken into consideration the complexity and cost of implementing PayPal's Payments Pro api vs Stripe's simpler JSON api.
The biggest difference is that MPL allows static linking while LGPL does not. While in the past this wasn't a big deal, it is important for iOS development since you cannot dynamically link to libraries in iOS apps.