No code problems as long as they are sized to maintain an acceptable cross/surface area. Which translates into use the right size and you are good to go.
Yellow are 10-12 gauge -- only one wire per connector -- the hole or opening in the crimp is a match for the screw or bolt -- use the correct tool -- and crimp into the split in the wire cup
They do come with the seam brazed, they are a big step up in quality and finish.
There are also little copper barrels, like a wire nut without the plastic part, and crimp instead of spring. These are the correct part to use when trying to get a stranded wire under something like a load center neutral screw bar.
- Trivia note - NASA uses terminal lugs instead of soldering, whenever possible.
Completely personal opinion, on wire terminals and associated parts.
I do not use the generic wire terminals with the plastic 'strain relief' covering, like those shown. They rely on the crushing of the plastic to insure proper wire contact. The plastic in these things is not engineered to crush,'just right.'
If I wind up in a situation where they are all I have, I pull the plastic off of them and use them without. This also allows me to see if the wire insulation jacket really meets the edge of the connector, to make sure all of the wire strands made it inside the barrel of the connector, and to check and see if or how much the seam opened.
Heat shrink after, if it will help with strain relief, or just look nice, is the way I finish them.
The right tool, the 12 in 1 tools sold right next to the terminals, are just not good (except for the screw cutter in the Greenlee brand one, thing works great, I carry one for just that reason.)
The Klein 1006 is the best generic terminal crimp tool of its kind. It 'feels right', it has good weight, it is not stamped sheet steel, the crimp forming nests are supported and sized well, and under $30 on the home depot web page.
If you must use insulated terminals, and there are valid situations for it. The Klein 1005 is made to crimp both insulated and non-insulated connectors.
Wire Strippers, I know real men use linesman's pliers for almost everything, but sometimes, they are just not the right tool. Klein 11049 are designed for Stranded Wire 8 to 16 gauge. You have no idea how wonderful the difference vs. using strippers for solid wires. They have 4 pair in this series big and small in both stranded and solid.