Here's my puppy buyer's experience on off lead. He had her off lead for about 6 months. He lives in nothern BC, so it's quite cold most of the year. As soon as it started to warm up-I'm talking around 32 F- she took him on a merry chase for an hour and a half. He said he'll never do it again. He also thought she was reliable, he knows different now.
One of the top winning obedience Basenji's, Sparky, is 15 years old. Mary would still never trust her off lead, as she knows it's just a chance she doesn't want to take. Usually, when a Basenji sees something that is more interesting than you, which could be a leaf, they are focused on the task and not you.
Another woman had her Basenji for about 5 years. He took off last fall and has not been seen since. And she also thought he was reliable and a momma's suck.
It's your choice, but just be aware of the consequences that could happen. Even the most reliable Basenji is really, well, unreliable!