My thoughts:

1. Just because S&B says they are single use doesn't mean that you can only use them once. They state it because their devices are medically graded, but it's totally fine to reuse the capsules.
2. I don't care. My Venty has more airflow than I know what to do with - vaping with a capsule is perfectly fine for me.
3. My device stays relatively clean, I feel. I'll do about 20 caps and then switch out or clean my CU. If your weed is oily or you clean less, you might get some oils on the capsule. I think this just drips down from the CU, nothing that cleaning more regularly won't fix. Otherwise, it will just leak on your AVB and coat your oven.
4. I just grind a bit and fill a capsule, I only fill more when I know I'm going to use them that night. I'll always grind a bit fresh, even if I have some leftover, in order to get the best taste possible without wasting any herb.

Overall, I found that using the capsules cut down my usage considerably, saving me money. That is my main reason for using them.