Are you planning day 3 or day 5 transfer?
The risk of multiples is significantly different between the two
With day 3 embryos the possibility is there, but not massive. Most clinics wouldn't push an eSET policy for day 3-ers.
With day 5 blastocysts it's a different story. The likelihood of getting pregnant doesn't, counterintuitively, go up by much if you transfer two blasts, but if you do get pregnant the likelihood of twins is 50%
At my clinic if you're under 37, it's your first cycle and you have good quality blasts, if you want to have 2 put back you have to sign a waiver saying that you're doing so against medical advice.
Have your clinics shared the eSET materials? This website is tremendously enlightening
http://www.oneatatime.org.uk
I put back one blast, but would have done 2 day 3-ers
I am now nearly 10 weeks pregnant with a singleton 
When you're going through IVF the prospect of a BOGOF two for one special is very appealing!! But the reason we're doing it is because we want a healthy baby at the end of it
The morbidities associated with twins are pretty significant. It's not just whether you're prepared to care for two babies, but whether you're prepared for going on mat leave at 6 months, or to have a long stay in the NICU. Worth thinking about carefully