I've used airbnb quite frequently in the last few years. I've rented both apartments and rooms. I've been very pleased. We've used them in Boston, San Fran, LA, San Diego, Paris, Bath, London, Florence, Rome, Venice...all over. I've never had an issue...but - one thing I do is make sure to read all the reviews (you said the accoms both have great reviews). If people complain about too hot/cold, dirty, noisy - I tend to pass those over.
I also check to make sure they have the amenities I am looking for - kitchen, non-smoking, air con, parking if needed, laundry facilities. And if the option is available, sometimes they have google maps so you can have a look at what the neighbourhood looks like - if it looks dirty and full of graffiti, I tend to pass. I also like to make sure it is relatively close to public transport. We've had some really nice places for great prices (we just had an amazing apt within spitting distance of the Colosseum in Rome for 3 people - under 150 euro a night - never would have found a good hotel in that area for that price).
I've had hosts (when we've rented rooms) who were everything from - here's the keys, do your thing, to one lovely lady who cooked us supper and took us on a drive the next day to see something we would have missed. And we've had some lovely apartments. I wouldn't hesitate to use airbnb. But the biggest thing for me is READ THE REVIEWS!
When you rent the accom, you do pay up front. Airbnb holds the money until a few days after you have been there in case of any disputes. Also, if plans are not totally firm, try to make sure that the person has a less strict refund policy. Some - as soon as you make the payment - if you try to cancel, they may not refund your money if they have a very strict refund policy (even if it is months away), so keep that in mind if you aren't 100% sure about days or the area...there are some with a refund policy that may let you cancel up to 48 hours before or a few weeks before...they may or may not refund the total amount. That being said, I've never cancelled any of my choices. I had a lady who double booked and had to cancel a night - she refunded and offered 20% off the next 2 nights if we still wanted to stay. I just booked a hotel for the cancelled night, then we did the other two as planned.