And it's because My Excalibur Vixen with a Red Dot scope is such a nice piece of equipment. I'm pretty new to shooting crossbows, but within the first month of shooting my excalibur I Robin Hooded at 20 yards, my groups are very tight when I aim at the same place, in fact I lose feathers because the bolts are so close together, but that gets expensive and time consuming to replace, so now I shoot at different spots when target practicing. I use a wheelchair and have limited use of my hands and no trunk balance whatsoever, but still I can hit my mark each and every time with my Excalibur, however I have not been nearly as accurate with other xbows. so for me excalibur is the only choice.
Good luck with whatever xbow you decide on, I'm sure there are many quality brands out there, but if you can test out an excalibur I'm sure you will be hooked within the 3rd shot.
Mike