As caption says..

1. Tinker's tools still effective in Betweenlands - I can use them without any penalties. Shouldn't that be fixed, should it?

2. Some tools maded from Betweenlands materials could be intresting..
   Let's say:

• Octine = Additional fire damage / chanse to lit on fire / Raising light level around player
• Syrmorite = Weakness debuff / Slowness debuff / Durability buff, or something more intresting
• Sulfur (as modifier) = Additional blast damage / set ground on fire

...and etc.

Great, but how can I use Octine to make TiC tools since they are no more effective in Betweenlands, as you recommended? Is it possible to make some specific ways to treat metal in betweenlands? I mean, it might be something completely different from TiC.

1 will likely happen eventually (if there's not a blacklist for tools already), but 2 probably won't happen as it'd be a lot of work for no actual payoff for the mod itself.

@WhatThePuckPT Wow, thanks a lot - didn't know about Pewter!
And yes, that's what I would like to see - some interaction with Tinker's

Second has already happened - there's a mod called Pewter, which adds TCon compatibility with Weedwood, Syrmorite, Octine and Valonite, all with special traits.

It would be great if there was a way to reduce effectiveness of Tinkers' tools without main parts made out of the dimension's materials, and have some modifier to let them be effective again - something like the Tar from Tar Beasts.

Much time has passed, Pewter works, but has been abandoned.

And it's still rather pointless, though: it doesn't give you any real reason to use betweelands materials imo. They have some minor advantages in there, but also suffer corrosion, which other materials don't.

Isn't Betweelands recognizing them as tools/weapons, or is TConstruct actually overriding Betweenlands' slowness effects?

IMO the minimum viable compatibility here would be to just slowdown all TConstruct items, and leave it to other modders to actually make materials which aren't slowed down. Like, if the ItemStack has the NBT data "betweenlandsCompatible", let it work. Not sure how exactly tool traits work, but they should be capable of setting NBT data.