For me to understand,
1) The lessons of the school offering ATPL(H) will be slightly different from the school offering ATPL. ( H - focus on helicopters )
2) No matter what school I chose I will take the same exams. (that are the same for airplanes and helicopters - but no questions for helicopters in the exams).
3) So if i chose the ATPL(H) I will propably have more to read (airplane+helicopter) but I will improve my helicopter knowledge.