As an owner of a Nomad II, I would say the Nomad II is a nice little piece of equipment (when it is working). Would I buy it again? NO. First, it is overpriced. Second, when it fails, the shipping to the manufacturer is expensive,
I have not found any information in regards to owner repair. This has relegated the Nomad to the status of emergency/expedient backup to help prolong its use. I bought a Yong Heng and appropriated an old SCUBA tank from my son for most needs.
If you need a 12 volt portable pump, I would consider one of the $250.00 range on Aliexpress. From all info, they are the same as the Hatsan. Should you want AC you can always add a converter for another $50.00 or so. At that price, the pump is more of a disposable item. Don't want do deal with China, go with a stateside Hatsan dealer for a higher price and some peace of mind.
These are my thoughts, and from your post, that appears to be the purpose of asking.