Use Bow roundabout quite a lot, and it isn't particularly pleasant - the early phase lights have done little to improve matters aside from being able to be marginally ahead of traffic if the traffic keeps out of the ASL and you aren't slow crossing the A12 entrance.
I use the flyover when the wind isn't too bad - it can get pretty gusty at times. Going up is easier that it might be imagined - mainly because the traffic on the flyover eastbound is light and there are two lanes. I see cyclists hugging the gutter on the way up and it makes me cringe as drivers doing 40+ don't bother moving lanes - I ride central in the inside lane to discourage this and make myself seen. My biggest issue is on the way down when I have picked up speed and there is a slip road to the left which drivers boot along and then try to barge in.
If you take the roundabout, my advice is to bear in mind that nearly all traffic in the left lane will be turning left onto the A12 slip road, so if you decide to go with the traffic flow as opposed to using the cycle lane then be really assertive and watch for idiots using the tarmac to left hook you. If you use the cycle lane then be aware that the first cycle light doesn't allow you onto the roundabout - you have to stop at the front of the ASL at second general light - traffic on the rbout has a green light and I have seen some near misses with cyclists assuming that the green cycle light allows them passage onto the roundabout. Oh, and finally they are p!ssing around at the exit of the roundabout Eastwards with what looks like a raised cycle lane. It may be OK when finished but at the moment you have to go around it and the road now narrows down.
The whole thing is a bit of a dogs dinner because TfL didn't have the balls to implement something that gave Cyclists and pedestrians (who aren't catered for at all) any kind of priority for fear of interrupting "traffic flow". They are now doing other stuff to the roundabout as part of the CS2 extension so I will try to remain open minded as to the quality, or otherwise, of the latest revisions. From using the rest of CS2 and Bow flyover it is somewhat difficult not to be sceptical.
Loads of cyclists traverse Bow junction daily and probably 75% I see go on the flyover. It isn't an absolute nightmare but one of those many junctions where the design is out of date and allows motorists to be speeding idiots if they desire (and some normally do).