Differences apart, it is important to discuss what they have in common as well. The common characteristics of these two spice blends allow them to be suitable substitutes for each other.  But it is important to remember that they cannot be utilized in place of each other regarding their primary usages. Hence, the tikka masala blend will not be suitable for marinating chicken for the tandoori dish while tandoori masala will not be a good fit to go in the tikka dishes.  Nevertheless, most similar ingredients can replicate the base flavor of each other. Therefore, the tikka masala blend can be used instead of tandoori masala and vice versa where these spice blends are required as secondary ingredients.  You may have to make simple adjustments, but still, they work better than any other options since they share the same roots.