Capacitors are very similar to batteries. They get charged up, hold this charge, then release it. The only difference between a capacitor and a battery is the amount of time it takes to charge and discharge. Batteries are slow to charge and slow to discharge. Capacitors charge and discharge nearly instantaneous.
Several other properties are similar too. For example, they wear out over time, they have a shelf life, they lose their power capacity when exposed to extreme heat, and they can fail internally and leak. The one thing that makes them different also makes them dangerous. Since they can discharge in an instant, this means the current and voltage they hold can severely injure or even kill someone who does not know how to handle them.
The quality of a capacitor is dependent on the materials used to manufacture the capacitor. Some materials are better than others. There are capacitors that have 5 year warranties and cost more due to the materials. There are others that are made from cheap less suitable materials and the capacitors can fail within months.
HVAC technicians have a wide variety of choices from their distributors and sometime just go for the cheap brand so they can make lots of profit. Not to mention they get more frequent return visits. Most consumers are not educated on the brands or what to ask their technician. Check with your technician if he/she offers any kind of part warranty for your piece of mind.