It isn't a back-rev at all, it is the next step in SFPs. There are several changes that were made to signaling and such that allows for 25Gb signal to be sent with the same power and number of wires as 10Gb. This means that 100Gbe uses the same power as 40Gbe, or only 40% the power of 100Gbe from early 2010's that were 10x10Gbe connections. Also QSFP28 and SFP28 are backwards compatible with QSFP+ and SFP+ which means you can get the faster switch and it will still work with the older components. All of these benefits at no more than 10% price increase per port than straight 10Gbe or 40Gbe, for 2.5x the bandwidth. There is a reason why 25Gbe is being adapted faster than any previous standard.I don't know if you're asking about home use or business use. If it's home use, good luck for Ethernet. 25g is mostly a back-rev to price differentiate between 40G gear and 10G gear. It helps keep 40G gear prices propped up rather than having to lower prices. Kind of like how 10K and 15K spinners keep getting put in SANs to prop up Enterprise SSD prices. Because of that, 25g gear is often newer gen than some of the older 40g stuff, and you might find better prices on first gen 40G gear vs. first gen 25G gear, thought the prices for QSFP cables may eat away some of those saving.
With generous discounts, a Cisco 9300 with Smartnet and a quarter fill of 25G SFP cables will run somewhere around $35K. Your VAR can get better deals than that, but it's going to have to be bundled with a lot more than that.