1. I agree, these are not terribly competitive, as they involve a lot more hours than other fellowships. This may change (a bit) as some cards fellowships will be ACGME approved starting in July. This means that you will then have a second board certification as a subspecialist.
2. TEE experience is a huge part of the fellowship. If it isn't DON"T GO to that fellowship.
3. TEE certification is a weird process. Anyone (yes anyone with $895) can take the exam given the last day of the SCA. If you pass this exam, you then become a "Testamur". A testamur can then do the following to achieve certification (As testamur status is not in itself a certification). Basic certification involves personally performing 50 echos, and reviewing 150 more. Advanced certification involves personally performing 150 echos and reviewing 150 more. If any fellowship won't easily get you to perform 150 echos DON'T GO there. Moreover, ALL 200 or 300 of the echos must be overread by someone who already has advanced certification, so this is hard to do in private practice.
4. I forgot one thing - Any echo done in residency does not count toward certification. I thought it would, but I was wrong.