Welcome to the Q&A Forum

In general that kind of implementation is correct. I do something similar for a client, who has a similar problem but more on the logistic side (different warehouse depending on the continent). Said that, considering that some products are only for the European market, I don't see useful to use an hreflang like the "de", which would target all the German speaking users no matter from the where they are... I mean, if they are in the USA, I believe that they are not allowed to buy products that are meant only for the EU geography even if they are German or Austrian. Regarding IP redirection, it's not an alternative... moreover, it's not an alternative obliging people to be sticked to one country/website because that it not allowed by legislation now. For instance, if someone from the USA want to see the EU site, he should be allowed to do it (this is also valid - obviously for Googlebot, as it is a user at the end). What you can do is working on the basket process, and there using the IP recognition for allowing or not a bought depending from the country someone is trying to buy a product or not. Doing so, you will also avoid the frequent dumping issue (e.g.: European buying in the USA because it is cheaper).