they’re hands down the best domain registrar on the interwebs. been using them for years.
I had to write something to interface with their API - it works but I could have used the OOTB solution in my router.
This does not change the fact that dyndns kind of updates is standard and they should support it to make their customer's life easier (and avoid coding an intermediate something to handle the changes). I wrote a webservice that translates dyndns requests into Gandi API calls but I would very much prefer avoiding to maintain that.