I have been bowhunting for 30 years and purchased an Excalibur Crossbow several years ago. Crossbows offer shooters that don't have time to practice, have health issues, or young hunters an easy way to get into the field with precision accuracy. They are a bit cumbersome in the blind or treestand for me. It now sits in its case in my closet and I switched back to a compound bow. It will however shootout to 60-70 yards with no problem. There are several manufacturers on the market that claim 1" groups at 100 yards. I just prefer the compound bow since it's easier to use in the field for me.
As for the bolts for most use 3 vanes in a helical configuration that helps stabilize the bolt with spin. The only one I've seen that uses (2) vanes is the pistol type that is not used for hunting. The two guys I hunt with use crossbows and have killed several deer with them over the years. They are powerful and all deer that have been shot you get complete pass through the animal. This usually means the blood trail is short and easy to follow.
If you do buy one make sure there are parts available and someone in your area can work on them. These things have at least 150-250# of stored energy. If they come apart bad things happen quick so making sure the strings are waxed and in good working order. Oh yea make sure to keep all your fingers on the grip while shooting it. These things would do major damage to your fingers if they get hit by the string.