Hi, I have just switched to Aptamil Comfort from SMA on the advice of my HV. The first feed took soooo long so we went and bought some new teats. She is 5 weeks old and we use Avent bottles too and were using a size 2 teat. The new teats we just bought and tried out last night were the size 3 'for thicker liquids' variable flow ones (using it on the slowest setting) and jeeeez did it fly down her throat!! It took about 5 mins to feed the poor thing almost 150ml and her abdomen was so swollen up with gas. She took ages to wind and just ended up throwing up and the same thing today. I even tried getting a pin and putting an extra hole into the size 2 teat. That still got vomitted up too. So, thats my experience so far...lol xx