Diving, or learning to dive, is usually more comfortable and relaxing if you have your own equipment. Dive school equipment is usually of a high standard but it is used far more heavily than divers would normally use their personal equipment. Dive school masks & snorkels have to fit many different shapes & sizes and as such are unlikely to fit as well as your personal ones.
When you purchase your own equipment you have a huge variety of styles available to fit virtually any shape face or body. This is something no dive school can achieve easily because not all styles will be used at the school.
There are many retailers across Thailand and the listed brands can be purchased at nearly all of those outlets.
Just be sure that you are purchasing one of the brand names listed and not an inferior copy.
For trade or wholesale enquiries you can contact Easy Watersports. For all your retail diving equipment needs stop by All 4 Diving or Water World Asia.