I'd hardly describe myself as either a pro or an expert, but I have recently been experimenting with Chestnut spirit stains on some ash and birch turned items and am happy to share my limited experience.
1. If you are using the tester set - be very, very careful when removing the little plastic plugs that seal the bottles under the lids. They fit very snugly and I had to prise mine out with a small spike - when they do pop out stain flicks everywhere - cover the top of the bottle with a cloth or tissue if you want to avoid stain splashes on your clothes, face, hair & the surrounding area.
2. Make sure the finish on the item you want to stain is first class. Any tiny sanding scratches or areas of slight tearout will be highlighted enormously by the stain.
3. I found that applying the stain using a cloth rather than a brush made for more even coverage off the lathe - but it's messy and wastes stain. For small items (boxes) I've had good results by applying the stain with a small brush or cotton bud while the item is rotating *very slowly* (under 100rpm) on the lathe.
4. Rub off excess stain with a cloth before it dries to avoid a patchy look.
5. The colours do blend into one and other as they are applied to the piece. The stain is based on cellusose thinners so applying one colour over another allows them to blend as new solvent is added with the new colour. Be careful off cross-contaminating the colours in the bottles, though - use a new cloth or cotton bud for each colour, or wash your brush in thinners between colours.
6. The colours dissolve into any cellulose-based product you may use on top of them. This could potentially be a problem if you want to finish with melamine laquer, sanding sealer or Woodwax 22 as darker colours could smear into paler colours on the item.
7. The colours look quite a lot brighter & paler on finished wood than they do on unfinished wood. I mention this because when I first got my set, I tested them all on a scrap of ash and thought they were all (except the yellow an orange) very dark indeed and probably needed thinning. This turned out not to be the case when I used them for real on a finished tool handle!
8. Splashes of stain do not easily wash off fingers or clothes
9. There's a "how to" in pictures here -
http://www.cobwebcrafts.co.uk/project1b.htm
showing how to get the blended effect.
tekno.mage