My thanks to Walter for emailing me - I've replied here so you can get it straight from the horse's mouth as it were.
It's quite acceptable to apply a shellac based product over a cellulose based product. This is commonly done when using Cellulose Sanding Sealer as a base for Friction Polish. Melamine Lacquer is simply a cellulose based, pre-catalysed lacquer.
There are no compatibility problems with this, but you really shouldn't use them the other way round.
It's a technique I've used many times (and shown to others...), especially in conjunction with our Burnishing Cream to get a very high gloss finish with lots of depth whilst still managing to avoid that 'plastic' look. The lacquer provides a tougher base than just sealer and as such will give a higher, longer lasting shine as the polish is unable to sink into the wood. (The sealer prevents most of this, lacquer stops it)
As to why do it?
I wouldn't on a pen or a bowl or anything that it going to be used as anything other than on ornament or would be only subject to very infrequent handling etc. It looks great but doesn't stand up to much handling. A Friction Polish finish is designed to be mainly decorative and works very well at that; it has a limited degree of resistance to handling and even water - but this is very limited. For harder wearing stick to lacquers or oils or in this case CA.
With regard to the 'selling more products' comment, which I accept was tongue-in-cheek, I understand the point and we always try to avoid this. Of course we demonstrate our products to the best of their ability and they are designed to work together, but when demonstrating I often say that you can omit certain stages if you want, but of course the final effect won't be quite as good. Still good, just not as good.
I hope that helps, I'll try to keep an eye on this thread and answer any other questions.
