Speed does not indicate effectiveness.
e.g.
Solve A = B * 2
The time taken to evaluate the value of A will be determined by :-
Program language - e.g Basic interpreter running a batch script from a floppy disc, or a 'C' compiled program;
The data type - e.g. floating point or 8 bit integer arithmetic;
The value of B.
Solve A = B * C
Even if C is given the value of 2, the time taken may exceed the time taken to solve A = B * 2.
I believe CCleaner is coded in C++, which is good for high speed.
Heidi may use something other than C++.
The language used has no effect upon how accurately it meets requirements,
only how fast it performs.
Before there was Windows, I had a 1 inch thick stack of fan-folded print-out listing innumerable DOS entry points for pretty will everything.
Some did similar things to others.
Windows NT probably has many more ways of doing the same things.
Perhaps CCleaner uses system entry points that are different from Heidi's chosen set.
Different entry points will probably affect speed, but this does NOT indicate effectiveness.
If you want to test effectiveness, I suggest :-
Create an empty TEST folder;
Select a TEST file, and copy to the TEST folder as file Test_Copy
Delete this test file from the test folder;
Use a file recovery tool (e.g. RECUVA) to confirm that the file is available for recovery;
Use a CCleaner Wipe Free Space;
Use the file recovery tool to see if the wipe was successful, or if it can still retrieve Test_Copy
Repeat the entire above test sequence, using Heidi instead of CCleaner Wipe Free Space.
I strongly suspect that no File recovery tool is likely to retrieve Test_Copy,
even if you used the fast wipe option of a single pass.
Some file recovery tools can focus upon a designated folder, which could reduce the search / report time.
A certain way to cut your test down from 24 hours to only 1 minute is to create 1 very small test partition for the wipe test.
There are a tremendous number of file recovery programs,
some of which may be more successful than others,
depending upon lots of things,
but a single overwrite is likely to stop them all.
Special multi-pass Wipe over-writing improves protection against sophisticated tools developed by the security services, especially if they have your drive physically opened up in their laboratories.
They probably can force the reading of a track with various amounts of offset from the nominal track radius,
and thus focus upon what was written by stray fields.
I believe they can also analyse the surface of the disc with specialised microscopes, totally free from any normal constraints imposed by the limitations of the Windows operating system or the electro-mechanical head position mechanism.
The professional thief or hacker is unlikely to have such facilities,
and even if he did it would take far more time to penetrate your system,
than it would to steal and attack 100 alternative computers that had not been wiped.
Regards
Alan