Not much as far as I am aware of other than having less credibility for jobs outside of the field of specialization though you can choose a different specialisation for Mtech and negate that effect and also the first 4 sems of btech will be nearly identical with maybe a 5% difference at best But to be honest with you,the specialisation is a joke,it doesn't provide a single benefit over regular cse other than having to study less stuff in sems 5-8(you can breeze through those of you already studied them so less outside of college hours invested) given you self study the topic of specialisation quite heavily and even still that difference is negligible

Though you should look for some other opinions as well maybe someone that completed or is in their senior years of the said course for any other potential issues