The national elections in NLD have a single ballot in the whole country, with 10+ parties who each get a column of their candidates on the ballot, and with one box for each of the candidates. In these elections for the 150 seats of parliament, often there are 200+ candidates listed total. As a result, the ballot sheets need to be quite large and so are quite far into the 'unwieldy' part of the handling spectrum.
This size issue also complicates verification and counting, because you have to verify that of all checkboxes, exactly one is filled in, and sorting/counting needs to do this for practically every ballot.
There has been some experimenting with changing the ballot to a 'party' and 'list number' ballot, where you fill in the party of your chosen candidate together with their number on the party list, but AFAIK that has not (yet?) been approved for wider use.