Nowhere near as strong as the very expensive 'official' product, but at this price, you can afford to replace the bags before they are absolutely bulging full! (Don't be tempted to wait until these ones get to that stage, or they will burst!) The paper material means that the bags can be composted, unlike the official version made of synthetic fibre, another plus for environmentally-concious users.
I still think there must be a market niche for someone to start manufacturing strong paper vacuum bags (like those that Miele used to produce), instead of customers having to choose between strong but expensive synthetic fibre or cheap but flimsy paper.