I only use CastinCraft resin when I'm completely out of 41.
I come from a boating background where Silmar 404 (same as 41, except 404/401 has structural integrity, but doesn't cure completely clear), are an industry standard that every "glasser" knows how to use.
I likely prefer 41 because of the cost factor. I use a LOT of 41 and order it in VERY LARGE quantities. The way I buy Silmar, I can buy it for less than 1/10th the price of CastinCraft ( if my market stays where it is now, I'll likely go back to 5 gal. orders).
41 SEEMS TO set up quicker, with fewer bubbles. BUT, I've also had excellent results with CastinCraft. If I poured 4 or 5 blanks per week, the CastinCraft (with a 50% off coupon and FRESH CATALYST - usually Michael's catalyst is very old) might be a better value.
I haven't ordered a single gallon of S41 in years, but I think the gallon price is now about $30 plus hazmat shipping, whick makes it nearly $50 per gal. With a 50% off coupon and a sales tax ID, sometimes you can get a quart of CastinCraft for around $20. I've had excellent results with CastinCraft, it just seems to "set up" a little slower. Buying it at a craft store, rather than from a distributor could mean that it is older, accounting for the slower set up.
I hope this helps!