Your consideration for fly ash bricks is justified and fly ash bricks are no doubt better than traditional bricks.
Fly ash bricks have following benefits:
- They are more durable.
- Absorb less water.
- Low energy consumption.
- No emission of green house gases.
Only thing is that they are costlier than the normal brick.
So if u r ready to shed an extra penny than surely you can go for fly ash bricks.