Since I posted this thread about the 2x Vixen Barlow from myastroshop I have found out more information about it. It is $49 because he is selling it for half price. I spoke to Steve and he said his supplier found excess stock of these in the warehouse so he is selling them cheap.
I did not order it before as I thought it was a $49 barlow. Now I know it is not such a cheap barlow I have decided to get one.
I ordered one yesterday afternoon and I recieved it this morning at 10am. This is the second time I have ordered an item from myastroshop and have to say they are very quick with delivery!
Tonight is the first night there has been a gap in the clouds since I got my Barlow. Just looked at the moon with it and the 5mm Vixen at approx 480x magnification. Looks really good. I didn't think i would be able to see the craters so clearly. It is shimmering a bit, but this should go away when it gets a little darker.
I haven't used any other barlow before so I don't have anything to compare it to, but i think this Vixen for $49 is a great buy.
Ok, tried looking at Saturn with the 480x. Nice big oblong blur. Oh well.
The barlow seems to be ok. It does narrow the FOV, but that is to be expected.
The 5mm Vixen LV (240x Mag) has a FOV of 45deg. The 10mm plossl I have is 52deg FOV. When I barlow the plossl to make it 240x mag it has less of a FOV than the Vixen. I suppose this is normal.
I have not seen any degradation in the quality of images, perhaps a little darker but thats it.
The narrowing of the field is not normal. A good barlow will preserve the apparent FOV of the EP.
Or are you talking about true FOV? It is quite possible that the barlow magnifies more than 2x, so you get a narrower true field than you would at precisely 2x.
I don't know exactly what you mean by true FOV. I just mean the actual image I see.
For example, comparing the vixen lv without a barlow which is known to be 45deg, I can see some stars to the edge of the FOV when looking at Saturn that are not visible with the 10mm in the barlow even though the 10mm is meant to be 52deg FOV.
true FOV: how many saturns wide?
apparent FOV: how many hand widths at arm's length?
It just sounds like you are getting more than 2x magnification out of the barlow with the EP you're using in it. Can you see the filed stop? (edge of field has a sharp well defined stop)
I think it was a sharp stop. I have just packed up the scope, I will have another look tomorrow night.
Come to think of it, I think the size of Saturn was a little different with the 5mm and the barlowed 10mm. I do not remember which one was bigger. I will check that also tomorrow.
Pls tell us how it does on other targets when you get the chance to try it out. 
