In my recent kitbashing clinic at Prototype Rails, I (again) left out description of a specific tool that I use frequently and love (too strong a word?) The tool is the Mission Models chisel. I have omitted it from clinic discussions because I erroneously thought that it or similar proxies were not available (I purchased mine directly from Mission Models over a decade ago; Mission is now defunct, although there is an unrelated Mission Models website that sells paint and modeling supplies.) On a whim, I searched google and discovered that not only is the Mission Models tool still available from Sprue Brothers, as well as on ebay, but UMM-USA also now markets a similar product (Ultra Micro chisels) in multiple size blades. These sites both cater to the military modeling community.
What is the value of this tool? If you frequently use an Xacto no. 17 chisel blade, the Mission Models and UMM-USA chisels are not necessarily direct replacements. Their advantages are a few. First, the cutting blade is far narrower than a no. 17 chisel, making it more precise and able to fit into tighter areas, where a larger wayward no. 17 blade could mar detail that one wants left untouched. Additionally, because the blade is created from hardened steel with a shorter rounded base, it is far stronger than a no. 17 chisel (I have had no. 17 blades snap in half; that will not happen with a Mission Models chisel blade.)
As noted above, there are a few different blades available. For the Mission Models versions, the blades may be interchanged in the handle and tightened using a set screw. The UMM-USA versions have integral handles that are similar to the Mission Models. However, rather than swapping out the chisels, you simply buy each chisel/handle separately.