Ever since I got my Vented Blast I'm dumbfounded as to why I even carry a kite bag anymore, Normally I have around 20 kites and many various line sets when I go to fly but lately I'm carrying all this crap only to fly 1 kite only.
I use the 15" power blast handles with mine pretty much left it stock out of the bag bottom outside attachment, Upper to lower line still attached to the inner pigtail.
I've taken it off a few times and tried different settings and I really don't find any change I'm at the point in flying where my hands and wrists have become self equalizers to whatever kite I pick up and how its set (kinda scary)
As far as the axles OMG I know what you mean you really need to try the vented its even better not only are they the flattest and lowest (Scott Weider like axles) I've ever seen but also the slowest or fastest.
I think the "Vented" version to me is the better match for the race rods it doesnt flap like a bird at all and even in low wind it performs like a SUL, Today in fact I actually setup the wind meter on the tripod and kept looking at it because I could not believe I was flying this thing effortlessly in 4-6 mph

without any real light wind moves it just grabbed the wind and went. Plus with the Vented you can use 90# line no problem till about 10-12mph when switching to the SLE and 150# is a better option.
I wish you were closer that I could just drive and let you try it but flying to the UK for a demo it would be cheaper to just buy 1 and send it (which I'm not

)
Do what you have to but I would suggest getting one at least to try and if you don't like it I will guarantee to purchase it from you shipping VAT and whatever, That's how confident I am you'll love it of course I already know you'll be ordering more for the team shortly after flying it