Can I use TC-DC58A with a DSLR?

It's a quite simple question but I couldn't find the answer. It looks this might be a solution to my longer range lens problem, combined with the 70-300 zoom. This one is intended for Powershots but as it has a 58mm diameter, it looks like it would fit to my lens as well.

Any ideas or recommendations would be welcome.

I wouldn't. Even conventional (between the lens and body) teleconverters introduce some loss of IQ. This, going in front of the lens, will introduce even more. Sure it'd physically be able to attach, but don't expect much more than you'd see from upsizing an image before cropping it.

Thanks a lot for you opinion Jon. I guess I need to start saving...