In general, I think the benefits of forming an LLC for a dive pro outweigh the cons. But definitely do your research. As others have pointed out, having an LLC does not protect your personal assets from legal claims of negligence should an accident happen while you are acting as a DM/dive pro. That being said, so long as you run your LLC properly, and if you adhere to the standards, common sense, and good judgement while acting as a dive pro, having that LLC might help establish that you do indeed take your dive business seriously and might be looked upon favorably in the event of a lawsuit.
The taxation issue may or may not be a benefit. It will depend on your personal financial circumstances. As others have said, a single-member LLC will be considered a disregarded entity and will be taxed as a pass-through, meaning on your personal income taxes. Yes, you can deduct qualified business expenses, but whether or not that benefits you will depend on how much LLC income you make, how many expenses you have, and whether it makes sense for you to take the standard deduction on your income taxes or to itemize. You will need to file a Schedule C for your LLC. Also, if your expected taxes on your LLC revenue meet a certain threshold you will need to file quarterly. Lastly, you'll need to show a profit at some point. That, of course, can be fudged a bit by simply not claiming some business expenses against your revenue, thereby showing a profit.
All of this means you will want to have a separate business bank account. There may be monthly fees associated with that. You'll also want to keep careful ledgers of your revenue and expenses. You might also want to apply for a business credit card. It is also possible to use a personal credit card for expenses and then reimburse yourself from your LLC account, but make sure you do it legitimately and keep careful records.