ddrescue is a reliable tool
When you clone with
ddrescue from a drive, and all partitions in this source drive are unmounted and swapped off, the process is very robust, and you can expect to get an exact copy with all bytes in the cloned copy to match the original data.
The exception is if one of the drives (typically the source) has bad sectors, that cannot be read.
ddrescue is better than most other tools to read damaged sectors, that are difficult to read, so it can copy more than other tools, often but not always every single byte (depending on the damage).
ddrescue can log the cloning process, and you can see in the log file, if there are any problems. If there is nothing in the log file about bad sectors, fine :-)
Exact copy or not
An exact copy is [usually] not necessary, depending on what you intend to do with the cloned copy. One example is if you want to recover data from deleted files: then you need also free space to be copied, otherwise free space can be skipped (or zeroed) in the cloning process.
Clonezilla is a tool that skips free space in file systems and swap partitions. This makes it faster but the cloned copy or image is still useful. You can restore to a system, that behaves exactly like the original system (except for recovering data from deleted files).