A northern suburban base
Sai Mai is a broad northern district of family housing, local commerce and quieter lanes. It is closer in feel to the outer residential belt than to central Bangkok, and it works best for people whose work, school or family is already north of the centre. A house can offer space, but the commute will be road based unless the address is near the Pink Line extension and its feeder routes.
The district borders Don Mueang, Bang Khen and Khlong Sam Wa, so its edges lead to very different daily routines. Sukhaphiban 5 and Sai Mai roads provide the main commercial movement. Side sois are calmer but less walkable. Inspect drainage, access and the route to the nearest main road.
Sai Mai is a family choice rather than a lifestyle district. It has local schools, markets and housing estates, but little reason for a central Bangkok worker to accept the distance. A car or motorbike makes the area far easier to use.
My verdict
I would consider Sai Mai for a northern family life and reject it for a speculative inner city commute. The area is straightforward about what it offers: room, routine and roads.