I do stand by my statements. Whether or not Sonic Port is vastly over-priced is a matter of personal opinion. In my opinion the price of the interface is more than it is worth. We probably disagree on that point. Where I think we do agree is that it is a good interface and useful.
In looking at interfaces that connect through the 1/8" jack (iRig and others) and the reviews I have read about them, I concur with you that they are not a good choice if you are looking for or need a high sonic audio quality interface device. As I have not tried the other interfaces, I am not in a position to judge them. I just am aware that lower cost lightning port interfaces are available for guitar, bass, and keys.
The Mobile Pod app will not work with interfaces other than Line-6 interface products Mobile-In and Sonic Port. This makes the app locked to Line-6 and thus I say it is a proprietary app in that you cannot use it with any other interface. I didn't buy Sonic Port solely for the ability to use Mobile-Pod, however, for the money spent compared to other software products combined with interface cost, I expect a lot more capability than Line-6 delivers.
I play 4-6 times weekly in various venues using the interface in conjunction with my iPad and various apps that far exceed the capabilities of Mobile-Pod. The interface is good, the app not so good; worth the price paid...? not to me.