This is no more dangerous to install than a custom kernel, because you flash it into the kernel partition of the onenand. This was one of the design goals - to install in a completely non-destructive way.

The other goal was for it to be completely self contained ie not require any files on Maemo rootfs or eMMC or an SD card (in contrast to multiboot.) That is the reason for the combined kernel image. The appended kernel image actually gets loaded into ram by NOLO (it thinks u-boot + kernel is one big image) - and then u-boot unpacks and boots it.

Since it might not be obvious, if you install this, the N900 keyboard does work - you can press any key to interrupt u-boot autoboot, and then do whatever you want in terms of loading kernel, setting command line etc.

Oh, also, nitdroid will need some work before it can be booted with u-boot, because it relies on multiboot scripts to set up some things like loading modules and setting up the filesystem mounts etc. All this stuff could be done by an initramfs though.