Whether you call them RangePlus, RangePlus-n, N150, or (misleadingly) Wireless-N, the premise behind wireless routers using single-stream draft 11n chipsets is that they provide a lower-cost alternative to Certified draft 11n routers. But in the end, it's a false economy.
Informed wireless buyers now know that you need separate WLANs for "legacy" 11b/g and draft 802.11n clients in order to have each not slow the other down. And if your older wireless gear doesn't support WPA2/AES security, that's an even stronger argument for not mixing the two client types if you want higher draft 11n speeds.
So if you already have a wireless LAN and are thinking to moving up to draft 11n, you need to add a second, draft 11n router, not replace the current 11b/g one, to get the highest speed from both your 802.11b/g and draft 11n clients. So why would you intentionally limit the performance of the dual-stream draft 11n clients that you're going to buy, by using them with a single-stream router?
The $10 - $40 difference (depending on how carefully you shop and waiting for promotions and closeouts) between a single-stream "N" and real draft 11n router is minor, compared to the money you'll be wasting for each draft 11n client you buy. Wasted, because you won't be getting all of the higher speed that dual-stream, Wi-Fi Certified draft 11n can deliver.
In closing, you're probably tired of my ranting about Cisco's misleading marketing of the WRT120N as a "Wireless-N" product. But there two more points to make.
First, I must admit that my tests support Cisco's claim that the 120N can provide "Double the speed of G when used with Wi-Fi Certified Draft 802.11n devices". But they also show that you don't always get the 2X improvement and that in weak signal cases, 11g clients will actually provide higher throughput and more reliable connection.
And finally, there is the matter of exactly what Cisco is promising when it comes to the WRT120N's performance. I asked Cisco the same question that I asked Belkin about its N150: "What is Cisco's policy regarding the interoperability, including expected speeds, of the WRT120N with Certified draft 802.11n products?". Here is the response (bolding mine):
"The WRT120N is WiFi Certified to be interoperable with ALL other WiFi Certified wireless devices.
Draft N certified devices (and as of next month, N certified devices) are interoperable with B and G certified devices, and since this device is WiFi Certified as G, it is therefore interoperable with all WiFi Certified devices."
In case you missed it, Cisco didn't directly answer the question regarding expected speeds. But if you read carefully, you'll see that they are saying that the WRT120N is only certified to be interoperable at 802.11g speeds, i.e. 54 Mbps maximum link rate, even with Wi-Fi Certified Draft 11n devices.
On that basis alone, I just can't recommend the not-certified-for-draft-802.11n WRT120N, no matter how Cisco tries to disguise it.