Looking for another budget option? This one, also from Chamberlain, is a good choice. With a powerful ½ horsepower motor, it’s reliable and rugged, especially paired with its industrial strength chain drive. The 100-watt bulb gives you some overhead light that guides you into your home from your car safely. It also comes with a pre-programmed, one-button remote that can be used over a long range. Plus, there are safety sensors that project an invisible beam helping to prevent the door closing on people or objects. And when the door is closed, you can rest assured it’ll stay closed and locked thanks to its Patented Security + 2.0 rolling code technology and PosiLock anti-theft protection.
Loosening or tightening the set-screws is the moment of most risk, since the end-wrench is a potential missile if you slip, and your hand is close to the cone. When the wrench is removed and only the rods are in place, it would seem that the worst that could happen is that the rod is flung out and the captive spring and cone rattle around, assuming you are keeping yourself clear of the rod's radial disk of rotation, and not leaning on the rod such as to fall into the apparatus were the rod to slip out of your grasp. The torsion shaft design has the virtue of capturing the mass of the spring and cones reliably on the shaft, preventing these parts from launching themselves as projectiles, even in an accident.
This opener is easy to install for most DIYers and comes with two remotes and a wireless keypad so you can open the door with a pin. If you are interested in having this smart-enabled you can purchase a separate kit to do so. The Safe-T Beam helps prevent accidents using a infrared beam that will open or close the door if a car is getting to close. 
You might genuinely need some extra parts when you thought you simply needed a broken spring replaced, and a good serviceman will perform a simple inspection to identify such parts. Nor is it unreasonable for a business to charge separately for a service call versus repair work actually performed. But the best protection for you as a buyer, being somewhat at the mercy of whomever you decide to bring on site, is to understand what is being done, and ask intelligently for a clear explanation or demonstration of why extra parts are required.

Garage Door Opener