What are some alternatives?
When comparing GRUB and Grub Customizer, you can also consider the following products
EasyBCD - EasyBCD is NeoSmart Technologies multiple award-winning answer to tweaking Windows bootloader.
PLoP Boot Manager - The PLoP Boot Manager is a small program to boot different operating systems.
Grub2Win - Safely dual boot Windows and Linux without touching the Windows MBR.
Visual BCD Editor - Visual BCD Editor - advanced GUI version of bcdedit utility. for Windows 7/8/10 and Vista
EasyUEFI - Manage EFI/UEFI Boot Options & Manage EFI System Partitions & Fix EFI/UEFI Boot Issues
BootIt Bare Metal - BootIt Bare Metal is a boot manager and partition manager software utility.