Fusionizer vs. Fusion Pack
Basically, the Fusionizer is an add-on for one of the two major mod packs, namely HSFX and UP3.
At the time of this writing there are two... three Fusionizers available, including FP069 that maybe should be considered a Fusionizer despite being named FP. We'll soon see why.
To better understand the difference, let's define a Fusion Pack as an all-in-one package that you can install directly over the stock game, right after the DVD (or download) install, without having to manually install the official patches released by Ubisoft.
Fusion Pack is installed in two steps: 1- install the stock game, and 2- install FP. That's it.
That is possible because all the packages that you would normally install one by one, have been repacked into one huge bundle. That's the Fusion Pack. And that's the reason why the download is so large.
Fusionizer as a part of FP
If a Fusion Pack is a huge bundle, a Fusionizer is only one of the elements included in that bundle. Let's take for example Fusion Pack 067, based on HSFX5.
If you were to install HSFX the old way, you'd need to follow 4 steps:
1- Install the stock game off a DVD or downloadable package
2- Install all the official patches in the right order, up to 4 separate patches if you installed off the DVD, 'only' two or three patches if you installed from Steam or similar.
3- Install HSFX 5.0
4- Install HSFX5.0.1 Hotfix
Fusion Pack 067 will install all that stuff for you, and then some more. That's the Fusionizer. The 'some more'.
That means, if you install all the stuff listed above, and then the Fusionizer 3.3, your game will be exactly the same as one modded with Fusion Pack.
Fusionizer Versions
As we have seen, Fusionizer3.3 is an add-on for HSFX5.
Much in the same way, Fusionizer4 is an add-on for Ultrapack3.
The main difference (at the time of this writing) is that while Fusionizere3.3 is available both as a standalone, and as FP067 bundled with HSFX and official patches, Fusionizer4 is only available as standalone. It will be bundled with UP3 as FP068 when UP3 Final is released, but until then, the Fusionizer will have to do
Which reminds me, why is FP069 actually a Fusionizer
Because we have defined a Fusion Pack as an all-in-one bundle that you can install directly over the stock game without having to patch it up first
FP069 can be installed over the stock game in the sense that it doesn't require an underlying mods pack such as HSFX or UP, but you *do* have to patch your game up to 4.10.1 before installing FP069, so technically it can't be considered a Fusion Pack. On the other hand, we have also defined a Fusionizer as an add-on for one of the major mod packs, and FP069 doesn't satisfy this definition either, so it's neither a Fusion Pack nor a Fusionizer. Actually it's a mods pack of its own. A light one, meant for on-line playing on stock servers
For more about FP069 see Versions link at the top of the page