Update: I contacted the seller and they facilitated a replacement even after the return period had lapsed, so kudos to them for that.It appears to work well for sealing Mylar. Give it plenty of time to preheat and I found even set to 3 worked for sealing 5 mil once hot.Previous: Unit has an electrical short between the hot and ground. Looks like the heating element conducts to the body. Trips the GFCI outlet instantly (thankfully!) and would blow a breaker if I didn't know better.temp seems to be all over the place, seals great one day melting the next, so use caution, ive lost several bags so far from it melting the bags. overall I like it better then some hair straighteners I tried that didn't work for me at all, but those were cheap ones so I might try a good quality one later... over I won't send this one back but I may take a temp reading on mine to see how much it really hold tempUnit worked well the first time. I sealed several mylar bags. Difficult to manage heat but once you get it tuned correctly it was great. I went to use it a 2nd time about a month later and it seemed to keep heating up even though the dial never went above 4-5. After awhile I realized it was cooling down and I never got it to reheat. Tried resetting built in breaker. Adjusting temperature. Unplugging for awhile. I bought this unit because it looked like it was built like a tank compared to others and it was priced accordingly.This is an update to the review.The seller reached out to me and promptly issued a refund. I appreciate that service. I may try another unit as I was very happy with the performance until what I believe to be the control board failed.I bought this to help seal my large mylar bags for food storage and minor league prepping. It was easy to use and seals well. The first one came DOA, but Amazon made the return easy and the replacement worked fine.I purchased the FDR-400 because I wanted to seal grains, beans, and peas in Mylar bags, the width of the sealer was great, and the price was right. There is a little bit of a learning curve as to how long to make the seal. In the end I settled on a temperature setting of 3.5 and about 4-5 seconds. I'm sure that depends on your bag thickness. On my third seal, the temperature had gradually crept up to the point that it melted straight through the bag. It made a real mess on the crimp, but it is still working. Before trying to get down a routine, I would suggest that you let the sealer's temperature equilibrate for about 10 minutes. You might also try stepping up the temperature gradually and practicing on a single Mylar bag again and again. Overall, I'm satisfied.Tried to use this for the first time out of the box and it won’t even turn on. I plugged it into the wall outlet and turned the heat dial to 3. Neither the power light on the built-in breaker (that I also tested) nor the heat dial came on. The unit never heated up. I also checked the wall outlet and its breaker to make sure they were working properly and everything was good there. This sealer was packaged and shipped defective. Quality control what?!?Edit: Ordered another one of these to try again. New unit turns on and heats up. Tried a test on the included mini Mylar bag and it seems to have worked. Will be using for my real projects later today.Don’t waste your money on cheaper products that won’t work, buy this product first. Works great on all thicknesses of Mylar. I am so glad I bought this and so sad I wasted money on other products before buying this sealer!! It deserves more than a 5 star rating.We stopped using this sealer shortly after we bought it because when you push the handles together the whole sealer moves forward changing where it actually seals.I battled with it for a whole afternoon. Only 2 setting on this thing worked: it would either warm your bags and NOT seal them, or liquify them at a higher setting. Do not buy.Excellent product- PROFESSIONAL quality with great temperature control. Can adjust to Carly’s material and seam requirements. Great buy. Highly recommend