Pros:
- can contain more fish in one tank
- DIY ones are very affordable
- can mix and match males and females in different sections (1 per section)
- far easier to heat and clean because you only need 1 heater and possibly two filters (depending on size of tank). This is unless your dividers don't have holes enough for water to flow between
Cons:
- if you used the "Do It Yourself" ones: If constructed poorly, they can fall over, break, not fit 100% properly
- you either must build the DIY ones far above the water line or drop the water to prevent jumping
- Mixing males and females have been (in my experience) reported to increase likelihood of jumping
- Some people don't like the look of the DIY dividers and think it looks tacky
- "official" dividers can get expensive and some people don't like the look of them
You can use silicon adhesive to stick the DIY dividers in, but you'll have to use an exacto knife and dissolver to remove them