I've ordered several batches of LED's via ebay and so far I can report complete success.
1st - they're cheap and they have to travel a long way to get to my trailer so I gotta be patient.
2nd - You're buying from China. Yeah, but I'll bet they all (or most of 'em) are made there no matter where they're shipped from.
3rd - You gotta choose carefully. There's 3 things I look for:
1) base, yeah it's gotta fit
2) color (measured in Deg Kelvin or K)
3) brightness (measured in Lumens)
For incandescent bulbs I like to get a color of around 3000K which I think is a "comfortable" color and is described as "warm white". I won't buy an LED replacement that has only the description of color as "warm white" alone.
For just a replacement bulb I try to match the Lumens as close as I can.
A quick Google search yielded this bulb performance table
Looking at their spec for a 921 bulb I see 105 Lumens which sounds low but the note at the bottom claims that an incandescent bulb output drops by about 60%.
When I bought my first replacements I did the above and only bought one. Installed next to a standard 921 I could tell very little difference, more importantly, the Bride approved. So I ordered enough to replace all the interior bulbs. When we traded for the 5th I bought more of the same to replace my 921's and shopped for replacements for the halogen bulbs the new TT had (2 types). I found what I thought was a good replacement and ordered enough to swap 'em all out and they've proved to be a good match. I also order extras so I'm sure to have matching replacements.
Some folks report the cheap LED's may cause radio or TV interference but I haven't had any problems.