I have eheim pro II's and fluvals, so I cannot somment on the rena's, but I can say I like the eheim better than the fluvals. I've had (2) 403's - threw them out. One leaked like crazy and the other just died one day. I have up and running a 303 and a 304. Very reliable, but - the 403 is a pain to service because of the design, and the 304 which was easy to service all of a sudden had it's quick disconnect stop working, making it a pain also to clean.
As for the sand thing, I use prefilters - just olf AC filters I cut holes in. They fill up once a month or every other month on the eheim, so I just take them off, rinse them out, and voila.