Maerklin make expensive Gauge 1 models and also used to make a cheaper range called Maxi, which I think was discontinued a few years ago.
I can't comment about the "proper" gauge 1 stuff (though I do think it looks lovely), but I do have a Maxi 0-6-0 loco:
The scale is smaller than LGB (closer to Gauge 1 scale of 1:32) so they look odd (too small) against LGB stock.
The Maxi range are simple designs made mostly from metal. They don't have much detail, I think they were aimed mainly at kids or people with a fondness for old tinplate toy trains.
The mechanism in my 0-6-0 is pretty good, and will run ok on most G trackwork. It uses a similar pickup skate to LGB. I think the wheel flanges are not quite as deep as LGB, I noticed my loco would sometimes stall on the frog of LGB R5 points which use a metal insert in the bottom of the frog to assist with continuity. I don't think the Maerklin flanges could quite reach down to touch these inserts. No problems since upgrading the points to live frog!
The couplings are definitely NOT compatible, I found a way to bodge an LGB hook and loop onto my loco.
Be aware that some Maxi locos came fitted with a "Delta" module, which is digital system NOT compatible with NMRA DCC. Make sure the loco also includes a replacement plug-in plate to allow running on analogue DC. If this is missing then something suitable can be bodged up from copper-clad stripboard which will plug straight in. Once fitted with the DC plate they run perfectly well on LGB and other G controllers.
Bottom line is I think the Maxi locos are very nice simple toys, probably best run with other Maerklin stock rather than LGB or Bachmann etc.
Don't pay too much for one: I don't know the current going rate on ebay but personally I probably wouldn't go beyond say £120 or so for another 0-6-0 like the one I have - and to be honest I bought only that one as the name plates are my wife's name so I had an excuse!