UK or Japanese Kindle?

Hi, my first post here, just before going to Japan.

I need help choosing whether to buy a UK Kindle beforehand or a Japan Kindle after arriving. My intention is to use it ONLY for buying Amazon UK books.

I know Amazon is regionally coded, but I wonder if the restrictions are applied based on your current location (IP address), where the device was bought, or your registration details.

Specifically, I'd like to know:
(1) If I buy a Japanese Kindle, can I register using a UK address and UK bank card in order to buy from Amazon UK?
(2) If I buy a UK Kindle and register in the UK with a UK bank card, can I continue to buy from Amazon UK even while being physically in Japan?
(3) If I buy a UK Kindle, can I take it to Japan and register a UK bank card/address while there, or do I need to register while physically still in the UK?

Anyone on this forum tried any of the above permutations?

My questions have just been resolved in an online chat with Amazon UK customer services.

The most interesting point is that you CAN buy a Kindle in Japan (much cheaper than in the UK) and register it to a UK bank card/UK address in order to buy Amazon UK content. (Needless to say, you'd be unable to buy Amazon Japan content in that case.)

You can also buy a UK Kindle and register it to a UK bank card/UK address even if you are currently (but temporarily) in a different country, and you can continue to use that Kindle to buy Amazon UK content whatever country you are in physically.

In other words, it all comes down to what Amazon believe is your permanent address (that is, the address registered to your credit/debit card) and not your current physical location or where you purchased the device.

I have also heard (not confirmed) that as long as you have an Amazon Japan account and another country's Amazon account, you can switch the Kindle back and forth, but in a very convoluted way. Sorry I don't know more than that. I would like to have access to both languages and have just not delved deeper into this matter.

Yes, it seems you can deregister your Kindle from one Amazon account and re-register it to another Amazon account.

Sounds a bit fiddly. And deregistering means you cannot access content in "Your Content Library" of that first Amazon account. If you were going to switch accounts frequently, it could be better just to have two Kindles...

Amazon.co.uk Help: Register Your Kindle

A similar Help page must exist on other countries' Amazon sites.

We recently had a poster who wanted to buy Japanese Kindles in bulk, for use in Europe. I believe he said the reason was that Japanese Kindles have more memory than those sold in other markets.

I believe there is also some market crossover, with many titles being simultaneously available through more than one regional Amazon.