All bullnose corner tools can adequately mark bullnose corners for trim placement. The location/width of the marks for trim measurement and placement is essentially the same for all of the tools available. You will see a small minority of negative reviews with all of these tools claiming that they are inaccurate. This is not the case! Making 3D models, injection molds and manufacturing is not cheap. It would not be wise to make a tool that is not accurate. These tools result in accurate measurement for the placement of bullnose trim with the tightest fit or least amount of caulking needed in between the trim and rounded drywall corner. Even if a contractor or DIYer wants the small corner piece to be larger (which will result in a larger gap requiring more caulk) that is still feasible by adding the dimension to either side of the trim marks. Accuracy is still gained by consistent placement of the corner piece on the center of the rounded corner and the widths of the small corner pieces will remain consistent assuming that the individual can use a miter saw with precision. All of the tools are designed for ¾” radius corners as these corners dominate the construction industry.
Some differences in the tools are listed below:
BullnoseBoss - Multi-purpose tool. Accurate trim measurement and placement. Accurately scribe a perfectly straight line down the center of a bullnose corner for paint color transitions.
Orange tool - Accurate trim measurement and placement. Securing (nailing) the tool to the corner is not beneficial as It would be a more time consuming. In addition It is much easier to measure from an inside corner to an outside corner, not the other way around. Sometimes it is necessary to measure from an outside to outside corner, however, the location used to hook/hold the tape measurement is not in the same location as the tool’s trim mark.
Red tool - Direct knock off of Orange Tool. C’mon man/No comment.
Black tool - Accurate trim measurement and placement. This tool allows you to mark the baseboard and corner at the same time (for baseboards only as chair rail and crown molding would be suspended). This could be beneficial, however, the carpenter will have to carry trim in and out of the residence and have it close to size prior to marking in some cases.