... well, thats exactly what i have on my 1st holga and I have no probs at all. The film stays flat, no extra light leaks and i get great negatives. In fact, sometimes i prefer i to my other holga with the factory made 6x6 insert.Also, just making a 6x6 mask by cutting out the extra material in the original 645 mask and using just the rim is not enough.
The best thing about holgas is to just try and see - new ones are available at very low prices on Ebay so it's not really that much of a problem if it doesnt work out. If anyone is thinking about getting one, dont wory about anything said here, just get one and try it out for yourself :wink: