Hi EStreeter 04,
I haven't been near this forum for quite some time. To be honest I gave up with it after I tried to post a review with some pictures of the Advanced elements convertible but it wouldn't let me.
In relation to the inflatables I would go for the Advanced elements almost every time. It is very stable in the water and you feel totally safe at all times. It tracks very well and cuts through the water very easily. I have been on 6+ hour paddles and not been tired at all. In choppy conditions on lochs or on the sea it handles almost as well as most hardcase kayaks I have seen. The Sea Eagle is unstable in windy conditions as it sits very high in the water and it is very easy to find yourself spinning around in circles, unable to control where you want to go. You also feel as though you could easily end up in the water in these conditions.
Manoeuvrability goes to the Sea Eagle. It is incredibly nimble and can turn so quickly making it great fun on rivers or on calmer days on the lochs. The quality of the workmanship and materials on the Advanced elements is superb, the Sea eagle is obviously a totally different design but the materials and workmanship again are very good.
The convertible is a bit more fiddly to put up than the sea eagle but not really that much and after a couple of times you can have it from the car to the water in 15 minutes - same time as for the Sea Eagle.
If I can be of any further assistance let me know.