Traded in my mid-range M1 Air for a base M4 13" in silver. It feels faster than the M1 and the 16GB keeps things running smoothly. Screen looks great, love the MagSafe charger, and build quality is excellent. When the M2 Air came out, I thought it felt flimsier than the M1, but no issues with the M4. This design makes it easier to open with one finger, and that's something I strangely appreciate as it feels better engineered.
My other half has decided to keep their M1 because it's gold. 🤷♂️
Trade in through Apple was quick and easy as always, and I really appreciate how they give you 14 days in case the new one doesn't work out. Regarding shipping, the M4 was sent via UPS 2-Day Express, and the trade-in return kit is through FedEx. Ordered Wednesday, M4 received on a Friday, trade-in kit received on Saturday.
For anyone interested, mine was assembled in Vietnam and it's the base model.