I agree Jac
The fact they expect ack for each payload Tx is wasteful of precious spectrum irrespective of any fair use policy any given back-end (e.g. TTN) seeks to impose - seems to have been spec’d/dev’d for a private use case (via a US based team?) and where some sort of audit or verification needed (I suspect). I expressed a view that (IMHO) a device like this should never have got out into the wild, without option to eliminate/reduce need for acks, and didn’t get much push back from contacts. What were the engineers/product guys thinking?! 
Hopefully something is coming that may make these devices more user, network and socially (from spectrum use POV) friendly. see my comments on another thread here
There are also hints of some variant with expansion of (external) sensor capabilities…if/when they get it ‘right’ it looks promising…