This is a good product that can help your swing tempo and sequence. I don't believe it is game-changing, but you will be happy to have one. The price feels a bit much for what it is, so it might be worth looking around for a used one. I'd give this 3.5/5.0 stars.
Not Obsessed: EyeLine Golf Speed Trap 1.0
I bought the EyeLine Golf Speed Trap to help promote a more in-to-out path. Despite a clever design, it was a purchase I regret and do not recommend you spend your money on it.
Obsessed: Arccos Caddie Smart Sensors are a great product for obsessed golfers
This is a no-brainer purchase. If you are obsessed with golf and want to improve and have an assistant by your side that more closely approximates a caddie than anything else on the market, Arccos is for you.