New install of ZenCart 1.5.5f - installed IH 4.3.2.
Decided to change to IH 5.5.0.
Uninstalled 4.3.2 and installed 5.5.0.

No 'Turn on IH' in Admin>Configuration>Images - just a reference to version number..

As per post #23 above, deleted the IH version row in the database..

Now have 'IH resize images' (set to 'yes') and the expected IH options..

But:

No IH icons appear in Admin Category/Product area (next to 'copy', 'move'..) and IH functionality only possible from Admin>Tools>Image Handler5

Is this a 'feature' or is there something I missed?