Shimano Cues

Pros

• I was surprised Shimano didn't move to the longer 1.1 cable pull ratio used by CUES which is far better suited for the tight cog spacing for 12-speed.
• The linkglide in cues will give you much smoother up shifts compared to the 5100. No more clunky upshifts, just smooth under power in both directions in my experience.
• I am glad Shimano seems to be consolidating their entry level stuff into Cues. That should be great for most bikes and then have the higher end stuff for the new features and weight benefits.
• I would hold out until you can find something with at least Shimano Cues on it.
• at this point in time I'd go for cues since Tiagra is being phased out and Cues has a wider range of components and compatibility and will be more durable since it's also aimed at e-bikes

Cons

• Sometimes a CUES-equipped bike comes out of the box and everything is great. Easy to set up, easy to adjust, easy for the customer to keep riding without it constantly going out of adjustment. OTOH, a lot of them come out of the box with...
• CUES isn't going to be any faster than Claris. If you keep the same crankset, your CUES top gear and the Claris top gear will be identical-- 50T front / 11T back.
• cues is just likely more heavy and more durable that's about it, probably doesn't shift any faster.
• Cues is fine if this is mostly a commuter bike or used on pathways rather than single track.
• If you don't want to wait, 10 speed tiagra is fantastic and relatively inexpensive. Sora 9 speed is also very good, but I quite like 10 speed. If you still want to do it, you'd have to consider the cost. I think the direction depends on...