I don't think ANY cleaner is safe in its DEFAULT state and in any case, should not be used by someone that DOESN'T review all suggested changes AND understand what each is being delete and know why.
Case in point, the Extension list. Most if NOT all will review files you have and then decide what extension entries are in the registry you are NOT using. Great, but at some point if you bring in a new extension and that doesn't have an install program for it that makes the entry in the Registry, you'll not be able to run it easily.
Same goes for things like HISTORY, MOST RECENTLY USE (MRU), and other temporary registry items. Some you actually want, like a browser most recently used URL list, and they get removed, no big deal, but it might have been something you would have rather kept. Many 'cleaners' pride themselves on reducing the registry and hence your boot times, but in reality, a lot of what they remove gets replaced very shortly.
The Registry can be large, it can be fragmented, and it can harbor a lot of unused entries. Unused entries doesn't mean you will not need them later either, just you are not using them. What these ARE good for is getting out 'left-overs', entries tied to programs you have deleted but they left registry entries. That said, some of these 'orphan' entries are very hard to find. Usually these are license numbers and personal data. Why is it hard to find, not to make them difficult to remove but so you can't EXPORT them and give them to someone else so they then can run the program. Cleaners can't locate these either.
Two rules if you choose to use any cleaner :
1) BACKUP the REGISTRY before doing anything!
2) KNOW what you are deleting and WHY!
Hope that what you do DOES NOT stop you from booting (yes, do something bad and THIS can happen).
If you really think cleaning the registry does anything (long term) for you, try and find SOME data that supports this. Yes, you can time your booting before and after cleaning the registry and it should improve but will it still have the same performance after 2 weeks of use or be back to where it was? SHOW ME THE DATA!!!
Some links for your enjoyment...
http://www.edbott.com/weblog/2.....-cleaners/ <<=== Maybe an OLD article but it still holds true....
So, in closing, I can also find a LOT of pages that tout using a cleaner, however all these are either by the provider or a shill. I still say 'show me the data'.
That said, I *DO* use a cleaner occasionally, and generally more than one, CCLeaner and JV16tools, and occasionally Glary... in EVERY case, each will find entries the other 'misses' (I do NOT consider this a good thing) and in ALL cases, I delete ONLY what I know an want. That said, even I've been fooled. Some registry entries are 'obscured', that is there is no clear connection to them. However a PROGRAM knows what it wants. No Registry Cleaner I know of scans every EXE to get strings and tries to match those strings to entries in the registry. I've at times lost use of programs until I re-enter the license or status/scores in games just because of this.
BTW, from what I know, when an entry is deleted, no cleaner compresses/compacts the registry (I could be wrong). So once the item is removed, it does NOT improve speed reading the registry.
OK, fire away at me....