ISTD is a widely recognized certification, which is quite comprehensive.
Advantages are, along with training delivery, course also covers basics (Organizational Behaviour, Manpower Planning, etc. ). This helps a trainer gain good understanding and concepts of content creation.
One more advantage is you will get to network with other trainers and faculty from the industry.
Hope this helps.
What the earlier resource person shared is absolutely right. ISTD Certification is widely accpeted around the world and across the sectors. Have zero hesitation in this regard. Certificate has lot of value.
My piece of advice is to know how to train, develop content and evaluation practically by standing in training sessions. thats more important. one has to prove as trainer by standing in training sessions and refine on regular basis. no alternative to this appraoch.
All the best