He didn't get files yet. Why you think it could unusable?

Any number of possibilities, logically corrupted sectors, physically damaged sectors, and so on. Any "forced" recovery
can and will mix good material with corrupt material.

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"Take care of thy backups and thy restores shall take care of thee." Ben Franklin revisited

Not necessarily. There is at least one way to separate partially or fully corrupt files based on bad sectors map.
Furthermore, no decent pro will ever advertise they got a 99% success and there is more than expected file corruption.

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

"...Any "forced" recovery can and will mix good material with corrupt material...." -- rolandjs
"Not necessarily. There is at least one way to separate partially or fully corrupt files based on bad sectors map..." -- labtech

Over in my neck of the woods, would you mind elaborating on this? As a newbie, I would like to learn more about how that is done from a specialist such as yourself.

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"Take care of thy backups and thy restores shall take care of thee." Ben Franklin revisited

All good tools are able to make files map and you can see if file got damages or not.

Never heard anything good about Ontack data recovery service, why people go to them ? Because they are highly selfpromoted in web with huge budget? Does it mean they are reliable?
We recieved recently case (samsung 2,5" M8) after Ontrack (Europe branch), where S-list module was intentionally killed when customer refuse the price.
Do we have any thier engineer here on the forum to understand level of DR skills?

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Angel Data Recovery

Most quality hardware imagers (and some software ones) keep track of bad sectors map. Consequently, they keep track of what files may contain some of these bad sectors. The really good tools, upon extracting the files, can separate the files with bad sectors from the ones without.

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

They reported that my transfer rate was really slow due to platter damage, is it normal and can the drive be 100% imaged?

Of course NO, because "... due to platter damage".

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http://www.alfadatarecovery.com

Yes, the process could be slow. It really depends on the specifics regarding how it is done, where, extent of damage, etc.

No, 100% is not possible due to media damage IF your files are in that area and IF that surface is accessible at all to begin with.

Overall, it cannot be done cheap, it will take a long time and typically with low chances of success after any competent companies have already attempted a recovery.

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

really sorry to bring my thread up again as I have been banned previously for asking regarding this issue. I am not a tech person and just want my data back. I am confused at what is happening and am trying to seek help here from you seniors.

The DR firm managed to image my drive but the result is in raw data form and is not readable as the files are all messed up. They said they are unable to read the data properly. Is there any recommendations anyone can make? Thank you once again for any advice.

nothing YOU can do about that
try to send it to another pro/company (but it will cost you - I believe -, since the drive has been opened already)