It is the exact same steroid, in pill form or in a water suspension. There are no changes at all to the molecule.
The only difference is in the method of administration.
One way is to take it orally, where it is absorbed in your GI
The other way is to inject it, where it is absorbed from your muscles.
In both cases, the drug makes its way into the blood stream, and makes its way throught the liver where the 17-AA molecule is removed, making the steroid active. Ther is absolutely no difference in action, or liver toxicity of the drug by either route.
One thing to note however is that the half life of winny is not entirely known when injected, as it takes time for the crystals in the muscle to disolve, and reach the blood stream. I believe UPJOHN - a Canadian Vet brand, has stated the product only needs use once a week. I personally have never tried that, and always used to inject my zambons on a daily basis.
As for oral winny, keep in mind that some of it will be destroyed or not absorbed in the GI, so more needs to be taken per dose.
The half life of oral winy is about 9 hours, so it only needs to be taken in two doses per day to be really effective.
On a dollar to dollar approach however, oral winny is always more affordable.