Assuming you mean Syn-Tac rather than Syn-Tek, they’ve been making rollers for offset presses for years. I’ve used their rollers on several small offsets and always been happy with them. Unless your Heidelberg has unusual needs, I can’t imagine you’d have any problems with Syn-Tac rollers, but I’ve never actually used any of their products in a letterpress application.
Assuming you mean Syn-Tac rather than Syn-Tek, they’ve been making rollers for offset presses for years. I’ve used their rollers on several small offsets and always been happy with them. Unless your Heidelberg has unusual needs, I can’t imagine you’d have any problems with Syn-Tac rollers, but I’ve never actually used any of their products in a letterpress application.
I have several customers that use them and love them. The best part is that they come with a new core each time you replace them.
I use them and they work well. I also have a set from Lith-O-Roll that are just as good.
Sometimes I wish they were just a little bit softer, though.