I use all of the following: an iRig Pro, two Focusrite Scarlett 2i4s (one 1st generation, which is admittedly a bit iffy, the other a 2nd Gen which is good) and a Scarlett 18i8 (including with a Focusrite Clarett Octopre 8-preamp/input interface expander that gives me access to a shed load of inputs - can fully mic up an entire drum kit!).
In some ways, I probably should have gotten an iRig Pro Duo instead of the second 2i4, but the 2i4 was available at a local store and the iRigs weren’t there anymore, so I ended up getting another 2i4. I’m quite happy with the 2i4 2nd Gen, but the iRigs are so portable and convenient, plus they sound really good, too.
For a non-iPad dedicated interface that will work with an iPad, you basically want two things: 1) that it is "Class compliant" (i.e., no drivers) and 2) that it will remember your settings when powered off.
Then, depending on your model iPad, you may need a dongle like the Apple ‘Lightning to USB3 Camera Adapter’ to hook it up, and then yer good to go.
Or, get a dedicated iPad interface like the iRig (there are a couple of different models, so see which one suits your needs best).
Note: My 2nd Gen is no longer Focusrite’s current offering. The 3rd generation replacement for the 2i4, called the "4i4" (since it now has 2 line inputs in the back - nice) is a little less iPad friendly than the older 2nd Gen 2i4 as they’ve removed three hardware switches/buttons and replaced them with software virtual switches that you need to either access through a computer or access via your iPad when using the interface with a computer.
However, for the OP’s needs, the 4i4 already has more than enough inputs so you could set these functions (principally, ‘Line/Inst’ and ‘Pad’) up once, differently for each of the two front inputs, and have everything you need right there in front of you in a dedicated input (i.e., put the Pad on on one input, off on the other. Probably just set both inputs for Inst as there are the two dedicated Line Ins ‘round the back if needed, tra la!)
