Amazon Newsstand

Magazines are ideal for digital delivery, which makes it downright embarrassing that Amazon can't do it properly.

The shopping works fine.  Magazines can be bought individually or through an annual subscription.  Note that not all magazines are monthly, so pay attention to the individual price under the subscription price - I've seen a couple that are more expensive per issue with a subscription.

In general, in order to read comics or magazines on a tablet you either have a huge tablet, really good eyesight, pan and zoom constantly, or you read the title a third at a time holding the tablet in landscape mode.  The last works best for me - you occasionally have to slide back up to read the columns, but you don't have to constantly adjust things or squint.  This works on other apps just fine - as outlined here.

Newsstand magazines are not available on the Kindle for PC app.  I won't even try it on my phone.  On the Kindle app on the Kindle Fire, there is not an option to read in landscape mode.  If you turn your tablet, it shows two pages in portrait mode, making things smaller.  The images can be zoomed a maximum of x2, which is still too small for my old-ass eyes and requires sliding the page around constantly.

Purely by chance I discovered that if you double tap on a piece of text it changes to a text and picture flowable format which reads like a regular Kindle title.  This mostly works, if you're not concerned with layout.  Magazines read on the original Kindle's this way as well.