There are many reasons T18-CSF25 is a highly optimal tip for SMD soldering.
Bevel tips have an oval cut surface, which is the perfect shape for holding a large solder bead and keeping it accessible. Angular tinned surfaces will hold relatively smaller beads before they collapse and they will suck the solder beads away from sharp corners. So you can get these sharp corners/points onto the joint, but the solder doesn't bridge/reach unless you are feeding more of it.
Tinned face only means the sides are chromed, which reduces the surface area of solder that is exposed to air. So the tip doesn't require frequent cleaning and the flux doesn't dry out as fast. Compared to a chisel, for instance, the chisel has that second surface covered with solder that is drying out the flux and making the bead go cold/chunky.
The chrome keeps the bead from creeping around onto the sides of the tip, so you maintain excellent control.
Somewhere between 2.5-3mm is the perfect size of a bevel tip. As you get bigger, the size of the bead gets too large vs surface tension, and gravity stats to collapse the bead if you accidentally get too much solder on there. The 2.5-3mm also holds big enough bead to handle anything, already. I have the 4, too, but it's actually bigger than it needs to be. I have not found any occasion to actually favor it.
Small enough to do most SMD soldering and drag soldering.
When drag soldering, you don't necessarily want to get the entire part to temp at the same time. That can suck a lot of heat into the board unnecessarily. The shape of the bevel tip means you are getting a lot of thermal mass onto a fairly small area of contact, and one which slides easily across pads/pins. The large bevel tip is very efficient in transferring heat; the shorty cSf tip is even better. Because of the large thermal mass, good heat conduction/transfer, and small area of contact to the board that you are heating up, you can use lower temps and still solder/drag-solder without any delay... keeping the solder from drying out and crusting so much longer than with other tip types.
The biggest drawback about using a TFO bevel is that you can't easily feed solderwire onto the top or side of the tip when holding the cut face parallel to the board. This is one reason for chisel tips. But the reality is that for 99% of SMD soldering, you don't need to feed any additional solder when using a 2.5-3mm bevel tip. The tip can hold enough solder for multiple SMD parts. You just apply flux to the pads, place the parts, pick up some solder onto the tip, then wave the magic solder wand around, coloring in the pads. And for through hole stuff, you can turn the cut face vertical and hold it against the leads/pin and feed solder onto the cut face. So a chisel might be slightly better for thru hole, but the bevel is almost as handy for thru hole and much better for SMD, IMO. At first, I would lay out solderwire on a board and pick it up from this board. But what I do ever more is have a solderwire feed attached to my microscope. It hovers a piece of solderwire above the PCB, in my FOV, where I can pick up a bit of solder as I need it.
A cut face bevel is also very good as pulling/sucking out bridges. Really second to none. When the face is wiped clean, it is very effective at sucking bridges. Sometimes, instead of using solderwick directly, I will wipe the tip on the wick then pull the bridge with just the iron. Also, you can lay the solderwick next to the bridge on flat FR-4 and put the tip down so it touches the wick and the bridge.
By controlling how much solder is on the tip, you control how much solder it leaves on given pads. For really tricky things that want to bridge, you will learn easy methods for controlling the amount of solder on the tip. E.g., to install FPC connectors, I solder the structural pads on either side, first, with a healthy bead. Then I wipe the tip and solder the pins. If the solder runs out, touching the tip to the anchor pad will pickup just a tiny bit of solder that is enough finish the pins without making bridges.
Another "weird" thing about using a CF tip is the residue. Burnt flux residue will build up all the way down the sides all the way to the very tip, because there is no solder layer there to allow it flake/wipe off. I just leave it alone and let it build up. I scrape it off only once in a blue moon.
These CF tips are one of the reasons I can't use a weller/ersa/pace. Only Hakko makes them. And they make more of them for the 888 than even the 951. On the 951, you can't get the 1.5mm, 2.5mm short, or 4mm, AFAIK. i don't think the 4 is very great, but the 1.5 (and the 1, which is also available in T12/13) is pretty great for point to point bodge wiring. Other manufacturers might regular bevels. And they might have a "spoon" or "gullwing drag solder" tip, which is a hollowed out bevel tip (worse for thermal transfer and not really that helpful, IMO) but even this won't be a TFO.
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