It really depends what do you want besides NetBSD. There was a long time you could use
GAG after installation to configure your installed oses and it worked great. Now I have Windows 7 and NetBSD on one hdd, i'm not sure if i use the windows boot manager for selection, but i saw never a problem with this configuration. You can also update your oses without modifying the mbr. So try the way with the windows boot manager and use easybcd.
I have another laptop with windows 10, where i will try to install NetBSD after a windows installation.