Mention "Hypersonic" and you'll get a real mixed bag of responses
Like Marmite, people either loved it or hated it. For sure, it needed a different approach to get the best out of it c/w normal slalom boards. But once dialled, it was a shed load of fun
The HS had a big range and is probably the only "one size for all" slalom board, great concept in its day.
The MK1 HS was one of my all time favourite boards. I had a D-ram 125 and a wood 105. Other than big sail slogging, the HS125 felt pretty similar to the HS105. I was using Gaastra Nitro's then, and used a 5.5m to 9.3m on both the HS105/125.
Now a days, a 5.5m on a 78cm board would be considered wrong as boards this wide are XL slalom. But the HS's huge double concaves allowed you to run on small or large fins, partly were its huge range came from. 9m sail, 78cm wide board and a 34cm fin (todays XL slalom can not do this) which mean't "fast" downwinders
It was very good in chop as its huge double concaves made feel like it was riding on a cushion of air, very comfy for such a wide board.
Not sure what type/size sails your on, but the HS likes cambered sails. A 7+m would really be the smallest size for the HS105. But this combo will take a lot of wind, 15k to 25k winds.
At £250, it could be cheap fast thrill's (in a good way)