I've used M-1 for years without a problem. I only cut one open once (so far), and it was quite intact and doing well after 4k miles.
I'll be cutting one open late next month with 8k miles. We'll see.
Search for Advance Auto Parts coupons, and you can buy them in bulk online, with in-store pickup, and get them for about $9 instead of $12. When I say "bulk", I bought 4 for me and 4 for my wife in order to qualify for the discount.
I should also mention that I've done UOAs with M-1 filters, and the insolubles came back as negligible in all cases.