If you already have sales via Amazon either through FBA UK or FBM UK to the main four (FR, DE, ES, IT) destinations then it is definitely worth serious consideration.
A number of sellers that I deal with encountered increases in Amazon sales of between 50% and 400% after they enrolled. However a lot obviously depends on your product, international demand and price.
The Pros Once they receive your goods, Amazon ships your products for free to the fulfillment centres throughout Europe allocating them on a demand / anticipated demand basis, meaning the buyer can get next day / faster delivery as well as qualification for Prime (subject to selling price) across Europe.
You can often increase your price because of the above, and the Amazon Pan European fees are often a lot less than if you shipped from the UK. This should make your prices more appealing to international marketplace buyers, and / or increase your profit margins or make you more competitive.
Amazon handles the customer service. No more Google Translate for messages.
Any returns are sent to the 'local' fulfillment centre rather than you having to pay for returns back to the UK.
Better chance of the 'Buy Box' as against shipped from the UK listings.
The Cons Before you send goods for inclusion, legally, you should register for VAT in the main four countries as well as the Czech Republic and Poland. However sellers I know have only registered with the main four and not had any problems.
While Amazon moves your goods around Europe, they may often be displayed on the listings as being unavailable and on 'Back Order'. This can affect sales, but if you send regular shipments to Amazon, not so much of a problem.
Differing VAT / TVA rates. If you sell VAT exempt items in the UK, these will probably not be the same across Europe. Also Germany has a rate of 19%, Spain 21% and Italy 22% if I remember correctly. You should build these differences into your selling price so that you do not lose out.
If you are already listing on existing ASINs in international marketplaces without problems then that is great, but still be aware of incorrectly translated listings that may not describe your product correctly. This could result in more returns, negative feedback and therefore a hit to your metrics.
Accounting costs need to be considered. Amazon used to have / still have a deal with KPMG where they would handle your European accounts. However knowing KPMG (my wife works for them) they are not cheap, even at a discounted rate. Prices quoted on the internet for 'local' accountants start at around 50 Euros for a quarterly submission, however how good these companies are, and the amount of info you have to provide to them is not available.
Being totally honest, all of my clients have said that it was a great way to increase their international sales, but it is ultimately down to you and your products.
E-commerce , love it or hate it, that's why we are here