Integral fittings are regarded as higher end options by many gun makers and clients.

From my reading over many years i'm not aware of much use of integral fittings by english makers. It seemed more popular with european makers and the old american makers like G&H and Hoffman.

Currently more makers around the world are making barrels with integral fittings. No particular pitfalls but it takes longer and you need enough skill to make good corners where the round barrel surface joins the various parts. Also take your time machining off the excess metal in the various areas. Alternate your initial cuts to avoid too much stress in one spot, that can cause a bit of warping.

There's no rules about when to use integral fittings, go for it if you want to try it. On the other hand if you are reproducing a vintage rifle in a strict manner then perhaps build it like the vintage makers.

I have done a few integral barrel recoil lugs but no integral sights. I have some images but no point posting any unless you have more specific questions.

Regards,
GABE93