I very much recommend the BoomKicker. I have a 1995 Sonic 30 (ULDB), a fractional with a large main and 13'' boom. The rig is Sparcraft and they, as a company, have been no help at all; but, the people at Seoladair were extremely helpful and responsive. They even helped me with the mounting issues I had...i.e. several mailings and a modified part. It finally ended up very easy with no holes drilled in mast and boom. This is a very clever device backed up by excellent customer service.
As for function, it does what I had intended at less than half the cost of the Spinlock Powervang...prettier, but requires "locking" at the device. The boom is supported in light air and the unruly main can be flaked by less than three people. I locally purchased a unit one size larger than recommended because I needed the extra length, then Seoladair Ltd.exchanged the supplied tensioning rods for a lighter "bendier" set. The unit is very lightweight with enough travel at the boom end to give me a wide range of settings, and it is easy to bend with an 8:1 purchase (added 2:1 cascade to the existing 4:1).
I have a Boomkicker K1000 on my Yamaha 26 tall rig. Installation was reasonable easy, the parts are extremely high quality, their directions are perfect, their in house help was excellent and in the end the boom kicker does its job of holding the boom up without need of a back stay requiring little effort to draw the boom down. In a word I am "delighted" with the end results. They are a fine company with a fine product....and it looks great.
I second all the above comments. I have one on my Hunter 26.5 and it works great. I already had a soft boom vang which you need to hold down the boom when you loosen the main sheet. The unit came with two sets of tension bars. I used the light ones for my boom. Easy mounting and removal for winter storage. Great product.