We support card data portability (we also use Spreedly to vault card as a service but we pay for it as an infrastructure) and in the case of Stripe we directly vault it in Stripe, as they do a great job of being friendly with customers and supports portability as well.
Apart from very detailed subscription management use cases, we enable hundreds of small things that come up as you grow beyond the first 50 customers - invoice based payments, coupon promotions for sales, credits (cash vs. promotion credit vs. proration credit) that finance cares about, detailed invoicing, accounting integration flow, taxes etc., while enabling pretty much everything with API as well.
Most of our customers find our product most useful once you grow beyond the 2 member founding team as the needs grow but you don't want to build spend your time building internal systems.
We share a lot of customers with Stripe / Braintree - Freshdesk, Study.com, Soylent etc.,
We also put a lot of focus on our customer support to respond within an hour for most queries and we generally deal with detailed use cases from non-technical members of team and we assist them.
This is a key area of focus for us, as that frees up a lot of developer distraction to address queries, as and when the cases arises. For an essential service like billing I believe it adds a lot of value, so we have built everything around having a very good customer support.
Happy to answer any questions.