Whelp, second edge of my HSS knives in my jointer are certainly passed their prime. Its to the point where i get burns on the wood if i pause for a second to readjust my grip. From the last year or so of reading threads about M+ versus Chrome versus Carbide, it seems like the carbide owners are very pleased with their investment. These knives are going in a generic italian 500mm jointer with a 4 knife head, and i almost exclusively process rough lumber. Unless the material was sawn skinny, i almost always plane both faces, so im not particularly concerned about the highest and best cut quality off the jointer. I just want my buck to go the farthest on my knives. I care more about the ease of feeding material and the ROI on my money for the next couple years than i do about glassy perfection off the jointer. That brings us to the cost comparison. M+ is about $16 per 500mm knife compared to freaking $123 per carbide knife. In other words, i can have about 16 fresh M+ edges compared to 2 carbide edges for the same price. Im sure carbide will outlast those M+ edges, but it might be 5-6 years before i reach the break point. I process maybe 2500-3500 bdft a year, and most likely see that number going down and down as the years go by(family time). My final question is, can i go down to two knives in a 4 knife tersa head? No matter what knife material i go with, i think i want to go down to two knives instead of four. for carbide, this is especially important because its $250 versus $500. I believe ive read people reducing knives in the cutterhead or running 'dummy' knives. One,can you simply remove the knife and run the head without the gibs flying out of the head? 2 knives is less feeding pressure than 4, correct? Not sure why they went with 4, i think the martin 54 had two knives for awhile.