I'm holding off installing any mods until the GECK tool is released to author them with.

This is because I'm concerned that non-GECK mods will cause instability in the game client.

But I've become aware that mods are being created without GECK.

Given my concerns, in the future when the GECK mods are available, how do I tell the difference?

How do I identify specifically the GECK mods so I know to download them?

And likewise, how do I identify non-GECK mods so I can avoid them?

Pretty much the only way you can tell is if the mod author specifies, or if the comment section is filled with people talking about how the mod broke their game (which you should look for anyway even if it is a geck mod)

Until the CK is out, I'm not sure if there's any good information on distinctive identifiers in the .esp data file.

I suspect the best ways to tell will be

1. The date the mod was first uploaded. If it's before the date the CK is released, then there's a chance the mod hasn't been recreated cleanly using the CK.
2. What the modder says about the mod.
3. What people post in the mod's comments.

But watch this space - once the CK is out, it may turn out there's an easy way to tell.

Just don't download any .esp mods that were released, or last updated, before the GECK's release date.

There are some solid non-geck mods out there. You really should give em a try.

Even Mods created with CK/GECK can cause instability. Iam not a big Fan of Nexus, just saying.