Yes, it turns out we do get Harker's here, online. I decided to learn a bit more about these combo meds as they can be useful when a firm diagnosis cannot be made or the ideal remedy is not available. I found out that the Avio 4in1 and the Medpet 4in1 are virtually identical containing Furaltadone 20% and Ronidazole 10%(or 7% for Medvet).
Both are said to treat coccidia, canker, paratyphoid(salmonella) and E-coli.
The Harker's 4in1 treats coccidia, canker, worms and external parasites...so a different 4 conditions. It contains Amprolium Hydrochloride, Ronidazole and Ivermectin. (this product won 'Best Bird Product at a recent trade show, according to their site)
I also looked at Harker's 3in 1 product which treats coccidia, canker and worms. (I believe I would prefer the 3/1 as I would rather treat external parasites...well, externally, and there should be no doubt about the diagnosis in this condition,

) It contains Ronidazole also and 2 other active ingredients that differ betw the liquid and the tablet version.
So depending on which 4 conditions are suspected one can decide which to use I guess...
Sorryfor the long boring post Don't know if this helps anybody else, but I needed to write it down to get it straight in my mind.