I remember reading a review/test of this pen from one of the national quilt teachers. I wrote and ask permission to repeat her post here. While the pen works well there appears to be some caution about it's use. S here it is. Both the original and her answer to me.

Hi Holice!
I posted this to a teacher group and told them to pass on the info. I really haven't published it anywhere. I've had a few people tell me that they did thoroughly wash for their test and the pen didn't come back in the freezer. I only washed fabric in the sink with soap doing some hard scrubbing between my fists. Do your own test if you want and let me know your results.

The original post.

I thought I'd give you all a heads up about Frixion Erasable pens. A student showed me hers at Road to California in January. She drew a line, thin but quite black, and then ironed it and the line totally disappeared. It looked like the coolest thing ever!
So I went in search of these pens, which you can get a Staples. I bought the pack that has three colors in it - black, red and blue. Being quite the skeptic about things that are too good to be true, I read the back of the package. In small print it says: "Do not expose to extreme temperatures (<14degrees F;> 140 degrees F). If pen is exposed to temperature that reaches 140 degrees F the ink will be colorless when writing. To restore color, cool to at least 14 degrees F and the ink will again write in color."
Aha! I said to myself. If you iron the ink it's going to be way over 140 degrees so it's going to disappear. So I took some fabric and scribbled on it with all three colors. Then I ironed it and, sure enough, all the scribbles disappeared. But then I put it in the freezer for about 10 minutes and all the lines reappeared. I left it for about a week and a half while I went travelling and today I tried to wash the ink out. It didn't come out with soap and hard scrubbing and not even after I put rubbing alchohol on it. So then I ironed the piece dry and all the lines disappeared and then it went back to the freezer and all the lines reappeared (perhaps just a bit fainter).
This experiment was enough to persuade me that these pens are too good to be true and even sort of creepy - the ink is always there even if you can't see it. I wouldn't use them on any fabric or quilt you really cared about.

If I had a blog I would have put this on there but since I don't any of you who want to pass on what I've written can feel free to copy and paste this post

Thanks for the info.

I just bought these, Staples had them on sale, but hadn't used it on a quilt yet. I even wondered about using them to write checks. Hot day and there is nothing written onthe check when they take it out of the envelope. Hmmm, not good.lol

I saw these in a demonstration and was in awe with the results. I was told that if put in the freezer the ink would reappear but the demonstrator said "Who is going to put their quilts in a freezer?" Makes me wonder if simply transporting quilted gifts in the cold winter months would cause the same effect. Something to think about!

I just don't get the concern about the ink reappearing when the quilts are frozen. Who does that? And ifmitmreappears while transporting them, iron them again. It seems to me that the advantages of this ink far outweigh this one disadvantage.

If you gave it to someone would they know to iron it or just think someone got ink on it?

I believe the big question is how cold must it be for the ink to reappear. In the north in the winter if the bedroom is kept cold during the day, will the ink reappear. I don't believe the issue is "putting it in the freezer" but normal use in cold areas.

It's good to have all the information on these pens then everyone can make their own informed choice. I for one LOVE my frixion pen. I use the black alot on small sewing projects. I use it to mark quilting lines on potholders, a perfect 1/4 inch seam line on some patterns, darts and hatches on sewing patterns etc. I have used it to mark applique placement on a wallhanging and quilting lines. I won't be using it on a full size quilt. I have other methods for marking my tops or I freeehand quilt them. I figure better safe than sorry but as I said, "make your own informed choice."

While I can see that a quilt might find itself in freezing temperatures while in storage or whatever, this doesn't concern me. I tested this myself. I wrote on a piece of t-shirt cotton and threw it in the washer with a regular load of laundry, cold water. It went through the dryer also. The sample came out clean, and sitting in the freezer did not bring the color back.

I love these pens and will continue to use them for marking quilts.

Any time your quilt is shipped, particularly during the winter, you run the risk of it getting cold enough.

Janet