The Apogee Jam is great - I've used the original and if it's silent recording (using ipad apps) and portability you want it's very capable.
I also have a Samson Meteor mic - good for recording a real amp, and only needs a camera kit connector and you're up an running.
This was done using the Meteor for gtr/bass and it's a big improvement overwhat I cd achieve with the Apogee.
If i was looking now (and thanks to your question I might well be!) there's lots more out there. I'd be seriously considering the following
- IK Multimedia Irig HD Pro. Similar to the Jam, takes a mic too.
Tascam iu2 dock
Focusrite iTrack dock
Focusrite iTrack Solo
All look like they provide a step up in the connectivity / versatility and are pretty reasonably priced.
I was a total novice when I started (in GB on iPhone) and have loved using the ipad for recording. Great fun and the interface is excellent, (at least it works for me)! Have fun and keep us posted.