I've used O&O Defrag a good bit, and had no problems with it. Defraggler is made by Piriform, so yeah same parent company as CCleaner. Also have had no problems with it either. I/O bit makes smartdefrag which I've also had no problems with. These are just the ones I've ran in recent years, and all in all I can't say that I see a huge advantage in one over the other. Maybe O&O, but that may be because I paid for it, but I wouldn't consider it to be a game changer amount of difference though. Most likely I've ran the IOBit one the most, in both the stand alone, and their entire utility suite (which gets to bloaty for my liking) IMO any of them are better than the older windows versions, but honestly I haven't even bothered with third party ones since Windows 7, and I can't tell any performance hit, but it is ran more routinely.nowdays too. FWIW, I always did the deep optimize, total defrag, whatever each respective company refered to it as for their best defrag routine (aka the longest time eater) the first time, and about every month or so after that.