I owned an original R4 a few years back. It didn't give me any issues then, so I opted to buy an R4i Gold since it could support microSD HC cards and the original only 2GBs.
I've ran a few homebrew apps on it with little difficulty (most were internet-based so I had to fix the WiFi settings via a ROM like Mario Kart DS).
The games though I had some problems in the beginning because after a few soft resets it'd corrupt the data on the card and I'd have to format it again, losing all of my games/saves on it (thankfully they were backed up). After reformatting the card one last time and using an unofficial firmware update from File Trip it got to work, although it took a uneccessary work to do that.
Game-wise it's compatible with a lot of them and if you run into issues there's always a patch out there somewhere. Not all the time though, and to rely on a patch/fix/run around method just shows the unrealiability of the cart itself.
So ehh, I don't recommend it. Sure, you can buy it and get it to work with most ROMs, but be prepared to do a lot of second hand work to get it to work properly. I'm looking into buying a Supercard DSTWO considering its high reviews, so I'd say go for that one if you can spare the cash on it.