IGCSE, Cambridge International's board, is chosen by Kolkata families expecting to move abroad or into an international school system, and its grading and exam style, tiered papers, coursework components in some subjects, and a global rather than India-specific curriculum, differ meaningfully from CBSE or ICSE. A tutor with genuine IGCSE experience understands Cambridge's specific assessment objectives, not just the general subject content.
Difficulty is not directly comparable since the curricula and assessment styles differ, IGCSE uses tiered Core/Extended papers in several subjects and often includes coursework. A tutor experienced specifically in IGCSE will understand its mark schemes better than one trained only on Indian boards.
Some do, since IGCSE and A-Level are both Cambridge/international qualifications students often take in sequence at the same school. Ask a tutor directly whether they cover the A-Level stage as well.
Many IGCSE subjects let schools or students choose between a Core paper (capped at a lower maximum grade, less demanding) and an Extended paper (full grade range, more demanding). Confirm which tier your child is sitting before starting tuition, since content coverage differs.