If low noise floor is your aim, stay away from these…
USB only proides 2,5 W power. That is not enough for a good mic preamp, if you also have to power a headphone amp and an AD/DA. Shure has alleviated that problem a bit by only providing 40 dB of gain. Maybe that’s enough if you use a top quality very high output condenser mic. But it’s not enough if you need to record reasonably quite sources with an average mic. I’ve never tried the Heil, but I suspect it will be equally weak.
There’s a reason why any decent audio interface has it’s own power supply. Apart from the wattage, USB power from a computer is very dirty. It requires a lot of filtering AND it also requires a voltage converter to go from 5V to 48V phantom power. That’s why some phantom powered mics simply don’t work with USB powered interfaces. Not enough juice.
If you intend to use an ipad, you have another problem. The interface needs to be USB audio class compliant. Some are, but not all. And most USB stuff dedicated to recording on ipads and iphones isn’t low noise, but depends on software running on the iOS device to filter noise. Unless you’re willing to spend a lot of money. Like the professional interfaces from Sound Devices. These are quiet, even at 100% gain.
“Standard” interfaces are more or less universal. USB mics are not. The can do one average job and fail miserably at most others, like very loud or very quiet sources.
And we still don’t know what you intend to record and how…