The loop holes on the Lomo product are certainly a good feature and not one that is on the long side of my Ortlieb (but the latter is very old and the design could be different nowadays).

The tiedown feature is also on the Overboard products, some of them anyway, via the inclusion of D rings - they may be even more useful than the loops, but the pricing is very different. The Overboard items vary in their "weatherproof" and "waterproof" designations; the latter use the same fold-over system as their competitors (which is simple in design, easy to operate and not too susceptible to failure). "Weatherproof" equates to the use of zips in the design which are more technical and, arguably, more liable to mechanical failure (just at the worst possible time, as per Murphys' law).

My main tip is try to get a bag that opens lengthways, rather than just at the end. Its infinitely more convenient for accessing your luggage.

The 89 litre (XL) ortlieb bag is huge. Maybe use it if you have no other luggage with you on the bike, but make sure the bike has a sturdy rack to take it.

If you have side luggage of some sort, I would really try to go for the 49 litre (L) ortlieb or less.

Not tried other brands, so cant really comment on them.

Definitely, although they're not without their issues. I used to find that in rolling up the bag I'd get the contents trapped in the roll unless they were packed in further smaller bags. To get round this I bought a sheet of plasticard (often used to stiffen panniers) and tucked this inside so that there is a small overlap at the opening. You then pack all your stuff as normal, with the added benefit that it keeps the bag stiff and open) then tuck one end over the other inside the bag so that it forms a roll and fasten the bag as normal. It also keeps a loosely packed bag stiff so it won't flop every which way. And you can pull it out and use it as a sit mat.

While I'm on the "top tips for roll-bags" I always seem to get air trapped inside. To get round this I've put in a Boston valve as used in inflatable boats.

http://www.bluewatersports.com/shop/...ton_valve2.jpg

I just melted a hole the right size with a soldering iron and screwed the two parts together, no glue needed. OK so the valve is designed to keep air in, but a push on the central core lets air out as you squeeze the bag.

The other perk when installed in a roll top bag is that you can use it as a pillow, just trap air in as you close the bag and then let the correct amount out for you as you lay your weary head upon it. I've even blown extra air in my bag, stood it on end and used it as a rudimentary stool and have contemplated trying it as an airbag jack by inflating it with a compressor, although perhaps not with my bike for the first attempt.

The blue bag is from a company called Overboard and that one is 90L.
It carries all the 'soft' items on my trip and was bones dry inside, despite Scotland's best attempts to breach it.
I got it from Amazon.

www.foxiles.co.uk/conkers.jpg