Is a five point harness booster seat or a plain booster seat that uses the cars seat belt shoulder & lap seat belt safe?

Forward facing

For children ages Four five six years

I'm confused about the safety

They have the adjustable car seats they say forward face but I've heard forward facing five point harness are dangerous and booster seats using adult seatbelt seam like not a good car seat. They have some booster seats with built in seatbelts are those good.

What are you guys using?

The convertible car seat with five point harness is too small that is why looking to change car seat up or if you know any convertible adjustable car seats for tall children?