Piriform's Defraggler is good for inexperienced users, but definitely not for more experienced user's. Defraggler falls short on it's actual job purpose. It tends to be slow during big defrag jobs and doesn't do a thorough job. Many files were left fragmented after it finished. I had to use a different defrag program to finish the job. Defraggler is probably good for small jobs only.
The inexperienced or average user may think it is great and be satisfied, but there are much better free defraggers available; Auslogics Disk Defrag, Puran Defrag, MyDefrag and Contig.
After 11 years of using (and paying for) Diskeeper, I have found Defraggler. Since I felt that Diskeeper was the best defragmentation option out there, there was no reason for me to look at any others. Within the past year or so (may be longer ago, I'm not sure) Condusiv acquired Diskeeper or they became the same company in some way. Since that time, I have felt that Diskeeper just wasn't/isn't the same quality as it once was. With that being said I tried Defraggler for free and am so impressed, I have upgraded to the "Professional" version. I am certainly not a computer genius or anything of the sort; but, I am a consumer of some software and Defraggler is one that works for me...
I have been using this little fellow for about eight months. I can't say it is better, or worse than other programs of this type. However, it does a good job and the little boxes are fun to watch. Watching the boxes is what defragging is all about, isn't it? It is a good program and when you compare the results with the Windows default they are just about the same. The speed is about the same as any other defrag program, so if it is speed you want when degragging, don't defrag your hard drive, just buy a new one when the old one starts to chug.
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