Both of these IEMs seem to have received fairly positive reviews across the board. I sort of feel like I'm leaning towards 5.0's, but if I'm correct, they're not immediately compatible with certain foam buds, such as the Shure Olives, which I'm currently using. I'm a little bit worried about the isolation of their silicon buds.
Also, how do the sound signatures compare?
Another thought-- I've heard that Heir Audio's 4.ai's and 5.0's are technically on par; they only differ in how they present the music. If money is a concern, should I be comparing 4R's and 4.ai's instead?
Last question (haha sorry): are there any additional fees that come with shipping Heir Audios to the United States?