Is there any specific motivation for using a complete-the-arrow
selection rather than marking an X or filling in a bubble?
I recall being told at some point that it was down to the supplier of the automated ballot reading machines. The oval method is used by one set of companies, the arrow by another. The choice is driven by patent & technology issues more than usability. However I cannot find any references for this with a quick google so take the anecdote with appropriate grains of salt.
According to a the election reform project there are problems with the arrow method in comparison to the oval:
Residual votes (and especially overvotes) are less common on
fill-in-the-oval ballots than on connect-the-arrow ballots. Voters
tend to be familiar with the task of darkening an oval (from
standardized tests and many government forms). In contrast, most
Americans have never completed forms that required them to connect an
arrow. Also, a common problem with connect-the-arrow ballots is
that arrows are found on both sides of a candidate's name (see #5),
creating confusion about which arrow to complete.