How good are the placements of IIIT Allahabad for an M.Tech? (Not a B.Tech)

Yes, any M.Tech person who is looking for placement is going to find one. Any person with an M.Tech background is pretty easily placed in brilliant companies like Goldman Sachs, Qualcomm, 1mg, Flipkart, Amazon, Daily Hunt, Razorpay, Swiggy, Phillips, etc. In case you are curious even in the least bit about your CTC, you need not worry as the highest CTC went up to 34 LPA. This was grabbed by people with an M.Tech background. 

Also, you will have better chances if you have great coding skills and knowledge concerning all your technical subjects. This can help you get placed pretty easily in any of these brilliant companies mentioned above. 

Having said that, you should also keep in mind that there are companies that reject people with an M.Tech background. NITs or IITs too, do not always accept people with an M.Tech background. 

Nevertheless, you would come across heaps of opportunities where you can showcase your skills and impress the panel.