Yes, the OSSC is great. I like mine, but it's not plug n'play like the
RetroTink products are. If you just need composite --> HDMI, then I'd recommend the RT2x Mini. It upscales 240p/480i --> 480p with zero lag, the most important consideration IMO. It supports composite & s-video. If you want a bump in video quality the 2x-pro supports Component or 2x-SCART supports RGB, depending on which model you get. And, if you want the ultimate, the 5x just came out, which upscales to 1080p/1440p with automatic phase. This way you don't have to dial in optimal timings manually like you do with the OSSC. It's just friendlier. It also has motion adaptive deinterlacing, looks better than the flickering Bob deinterlacing the previous RetroTink products and OSSC use. The biggest feature IMO is framelock and tripple buffering, which prevent sync dropout when the resolution switches between 240p/480i, like the pause menu in chrono cross. Again, the previous RetroTink procucts and OSSC don't have these features and drop sync in some games. It's actually a deal breaker for me, because it renders games like resident evil and dino crisis unplayable. You can get hit by an enemy when the camera shifts and sync drops!
Framelock only adds 4ms of lag. It cuts down on drop outs alot, but some might get through. If that's not good enough, you can turn on triple buffering which absolutely will prevent sync dropouts. It does add 4-20ms of lag, but that's all. That's usually unnoticeable. I'm sensitive to lag and absolutely hate it! However, 1 frame of lag is acceptable to me. I can feel it, but my brain will get used to it quickly. What I can't get used to is variable lag of 2+ frames. That's common in cheap upscalers and it renders retro games unplayable!
Still, nothing beats a CRT. Hands down it's the way to play any retro game that was designed with it in mind. Even on composite it's a great experience. S-video is a nice upgrade. Component is cool, but not really needed. If you can find a cheap CRT and have the space, it's by far the best and cheapest solution to playing retro games.
On a side note. I bought a G-Comp switch so that I could split my analog consoles to a CRT and upscaler for the HDTV. This way I can play on either one or both at the same time. For you european SCART users there is a G-SCART switch too. I thought about going that route, but decided to go with component since we never got SCART TV's in North America (I'm jealous). I could mod a TV's OSD for RGB and put a SCART port on it, but component is almost as good and readily available. That and getting cables for the consoles was easier. So I wet for an all component setup instead. The G-Comp switch accepts 8 component/Composite in devices and auto switches them out 2 component/composite ports. I use HDRetrovision component cables on any console that supports component and a few that don't (I RGB modded my N64 and SNES jr. I have the kits, but haven't yet modded the NES and Atari 2600). I have one hooked to my CRT's component input and the other goes to my OSSC (Currently). I will be getting the RT5x as soon as I can get my hands on one just because it doesn't drop sync and 1080p/1440p automatic phase is next level. And I like that it's plug and play.
To tell you the truth, I don't really use the OSSC that much anymore. It's just a pain to set it up compared to the CRT. And the CRT feels more authentic. From the OSSC it goes to an HDMI splitter to a capture device and my HDTV TV. With this setup the CRT and HDTV are in near perfect sync. I can play off either one with less than a frame of lag between them. And even my capture window is legless (Startech USB3HDCAP). But the capture device doesn't accept anything above 480p from the OSSC and the retrotink is more HDMI compliant. So it should play nice!