I have this seam guide for my 301. All the computerized machines I've seen opened up have the computer parts encased. A magnet couldn't affect it unless it was wide open. Maybe some of the very first ones aren't protected.

Great gadget!
When I bought my Bernina a couple of months ago it was one of the questions I had written down to ask them at the shop. I was so happy to hear that it wouldn't mess with my new beauty. I really like it for sewing the binding on as I am already trying to keep track of all the fabric edges and watching the seam allowance is one less thing to do.

Bought one magnet thingy and really didn't like it. Then bought 1/4 foot with the guide attached. Love it!

Used one of these for years on my old mechanical machine. Measure from the needle and place the magnet on the stitch plate. I loved it as I did all types of sewing so I could move it as necessary for varying seam widths. Have a 1/4 in. foot for my FW, so don't use it (or my magnetic pin holder either) anywhere near my computerized machine. No need to take any chances no matter how sealed innards might be!

I have one of those and used it a lot before when I was sewing. When I started piecing quilts I was using it but I found that I liked using a piece of masking tape along the 1/4" seam line a little better. I have an Elna...not a computerized machine. I'm hoping to save enough money to buy the Janome 6600 in the spring so I appreciate those who said to keep the magnets away from computerized machines.

I have a Bernina 440 and I emailed the company about using a magnet on the side to hold pins. They said it is okay and will not interfere with the machine.
I also have one of the above magnet seam guides and use it as well. No problems.

Ive never been able to use a full 1/4 inch and have a block come out the right size. Always have to adjust the needle for thinner seams. Some patterns more than others.

I use this all of the time and when I went to teach my sister to sew that was the first thing I bought her. I use my normal foot to sew with. You should check your feet to see what you have. You may have to adjust your needle to one side or the other if you have that feature but you should be able to use this with a normal foot.

You can buy these at Walmarts or Joanns they are around $5 and work great; really hold to your machine. I use a normal foot though without any problems.