My first order from Amazon JP was the yarn yoshis. They ended up being around $45, and tenso shipping I splurged for EMS because it was a present, was around $16, so around $60 with 3 day international shipping which was a pretty good deal. They came packaged great and in perfect condition. Great experience.
My second order was Dr. Mario, Olimar, and Bowser Jr. They ended up being around $31. I paid for registered SAL this time, the items were heavier so even registered SAL was $16. But then I got a message that the package was too big for SAL so I had to use EMS, which was $23. I was curious why these three amiibos were bigger than the last package, but there was nothing I could do. The package finally arrived damaged and the three amiibos were placed in the bottom of a cavernous box about three times bigger than necessary with no packing material. So I ended up getting the three for $54, or $18 each. Not terrible, but not great.
My main issue is that I now can never be sure how Amazon.jp will package things, which affects my shipping options and the total price. It may not be a big deal for some, but for me I don't like not knowing when I order something how much it will cost to ultimately get to me. If this doesn't bother you, then Amazon.jp and tenso are a great option. It takes a little while to set up the tenso account, but once you do it's pretty easy to use. Because you need a forwarding service the amiibos tend to last longer on the site than others and with the favorable exchage rate they are super cheap.
For me though, I've tried importing from some foreign sites and AmiAmi is the only one left I will probably continue getting things from unless I get desperate. With the recent restocks and higher stock numbers it just isn't worth the added expense and uncertainty.