Some people in fact use straight white vinegar, as it is essentially the same thing. A lot cheaper too. The only commercial products I'm familiar with are the MicroScale and MicroMark systems. I use Micro Set and Micro Sol myself.
How are you using the softening solution? Lots of people who report unsatisfactory results with decal softeners, e.g. wrinkling, are applying it before the wet decal has had a chance to set and dry (including me).
Through some trial and error, as well as according to advice I've found on this forum, I've found Micro Sol works best when the decal is totally dry, and then let the softening solution do it's work overnight. If there are still wrinkles or bubbles, you can carefully puncture the area with a needle or sharp X-Acto and then reapply.