Indeed you are both correct legally. I recall reading on some of those reciepts that if the wind was over 40 kts you were to get off their ball. Yeah right. . I was mainly responding to the poster who planned to anchor most nights. He may be like the fellow I talked to last month anchored off Marina cay on a charter who runs a week long excursion boat in Alaska in the summer. Obviously anchoring in the BVi is child's play for him.
But many chartering have little experience anchoring overnight on a vessel the size of the charter boat. Indeed when we had a boat in charter I got to buy a couple windlass. Some believe it's there to "reel" the boat to the anchor. I saw a cat that spent the night in pond bay a few years ago totally splintered on the reef. I've had a boat drag in Great Harbor, from the same exact location, same scope and anchor that worked probably 30 times. I've listened to skippers drag chain against the bottom of hull not knowing where the anchor was or having a spotter signaling.
I've seen a cat drop anchor in coral off Guana. Witnessed a chase to catch a boat that drug from Sandy Cay. Seen people anchoring in mooring fields or so close to outer balls they interfere. So for the average charterer I think a ball or slip is safer for his crew and the boat and the seabed.