Two other things to mention, is that the TF10 can be a really troublesome fit in some peoples ears. It is the only IEM I have ever owned that has given me bother trying to get a good fit with it and I am not alone in this. Also if you listen to any music that is sub-bass heavy the TF10 is not a good choice as it simply cannot reach low enough.
Other than those additional observations, Gilly87 has the comparison well summed up. Personally, I enjoy my TF10 more than my SE215, but they are nothing like each other soundwise.
I have the Excel spreadsheet from measuring the TF10 (The data behind the Headphone.com graphs, made and measured by Tyll Hertsons I believe)
The TripleFi 10 by Ultimate ears reaches 10hz just fine, and has a smooth curve up to +5db at 100hz, curving back down again and reaching -15db at 5khz... It can reach low enough, though it may not have a ton of emphasis on these frequencies if it's being compared to a bass heavy headphone. Using the EQ on either of your Rockboxed devices should enable you do adjust accordingly. Try a +10db boost at 30-40hz.
(Beyond the measurements, I've owned the TF10 for a year, listening extensively. Besides my Klipsch Image X10, it was the most 'bass capable' of the bunch. I have since moved on to an Audio Technica AD900, which is a brilliantly detailed and bright headphone (Neutral actually, but since ears hear treble better, it sounds 'bright')... It makes the TF10 sound muddy and dark unfortunately.)