Any recently performed hair transplant should give a natural and in most cases an undetectable look from the front. The lateral slit is an important part creating a natural result. If the hairtransplant does not look natural the doctor (and in some clinics the technicians) have simply done a bad job.
However, it may be mentioned that even if the surgeon has carried out a state-of-the-art hair transplantation a limited number of patients may have a surprisingly poor growth.
From the back a strip-transplant will leave a linear scar which in some cases can be rather visible and disturbing. FUE leaves hardbly visible scarring.