5c has its ups and downs for sure. Like you mentioned, it needs exact collet sizes, although it seems to have enough give to handle standard stock sizes. They are supposed to handle +/-5 thou. One advantage of 5c over er is that they can grip onto short parts right at the nose. Er collets collapse at both the front and rear so if you try to grip something right in the nose, it will collapse at the back and not grip correctly. 5c is also nice because it's extremely versatile. Any attachment you can think of with 5c on the back of it. Expanding mandrels, large step chucks, 3,4,6 jaw chucks, flat fixture plates, emergency collets, list goes on, including a 5c-er40 attachment which i will most definately have for gripping any size I want. Bit more run out in the 5c-er40 attachment vs just an er40 chuck, but not much. The draw tube is also something that adds pretty huge capability once investing in a pneumatic closer. A bar puller attachment is simple to add, then you can crank out continuous parts unattended, as many that will fit in the bar stock.