My daughter is 10.5 months and has never had a puree and never choked. She did gag a bit in the early weeks, but no big deal, they are meant to gag and she was fine. She also only has 2 teeth but we started BLW before she had any. They manage! It's amazing what a baby can chew without teeth. She has sandwiches, and chicken strips, and baked fish, and whole broccoli florets, etc.
Only you know what feels right for you, but the reality is, he won't be on purees forever and he'll have to master finger foods without choking in a couple more months anyway. So you can do it at 6 months or you can do it at 9 or 10 months. I think better to save yourself the hassle of all those purees and all that spoonfeeding and just do it earlier. The great thing about BLW is that you actually get to eat too! My daughter has been feeling poorly the past week and getting her to eat at all is a challenge, so she's been mainly eating yogurt, which I've been spoonfeeding her. Spoonfeeding is work! I barely get to eat my lunch because I'm feeding her the whole time. It's so much nicer to sit back and relax and enjoy your food along with them without having to be shoveling food in every few seconds. I've never been more thankful that we did BLW than I am this week and I can't wait til she's feeling well enough to eat normally again.