Hello! Our company uses handsontable and maybe I can contribute.
sample
row add/remove : http://jsfiddle.net/tdjun/p3gp0Lny/1/
header/row merge, cell formula : http://jsfiddle.net/tdjun/heo3xc04/
row add/remove & header merge : http://jsfiddle.net/tdjun/gtu2vbz0/1/
source : https://github.com/tdjun/Handsontable-MergeHotGrid
regards
tdjun