It depends what you mean by a performance issue. Most people who purchase External Images do so to speed up their imports and reduce how much space is required on their server, i.e. they buy it to improve performance.

However, if you run GT Metrix against a page with external images, because we use ONE image size, GT Metrix will report a lower score. If you wish, you can proxy your images through your server and have them resized on-the-fly and if you combine this with Cloudflare you can have the best of both worlds.

Less storage requirements, faster imports and no drop in page speed scores.