The Armstrong mast is a short 85 cm mast right?
I would never buy one of these, but apparently so many different views on this...
You are still learning and use a super short mast, but when more experienced, I think you would love the 90 to 95 cm masts most seem to prefer for overall conditions.
SUP foilers/surfers seem to like the short masts more, I guess it is because they need these in order not to hit the reef, and because they are not as sensitive to touchdowns as many of us kite wave foilers are, so when doing both this and kitefoil they prefer the same mast as used to, or because of cost naturally, having only one is a LOT easier
The Onda Kite 91 would be my advice to you, either that, or the same but with a 683 wing.
Almost the same, the 633 a bit easier and more surfy, the 683 goes better upwind and a tad faster - but in the same range and not hugely different actually so just choose what you think is what you will like in the future.
Of course I think (as I ride these) the KETOS are the very best, but also quite expensive, and I guess you would like a cheaper foil and with a plate mount, thus I recommend one of the two above, and you will have a perfect foil for years IMO