I've got the 10000xsc model and they are fantastic. Strong but light and line lay is something else with super slow oscillation, often think you've cracked off they cast that we'll. Winding the usual stamp of codlings up to about 3-4lb can be done without much pumping. Something that can't be said of the std ultegra which wobbles about like a eel.
Are they worth the money NO but there's not much else that offers what these do. Buying new from abroad is the way forward but be careful that you get the 2 spools as spares aren't cheap!
They do need to be looked after though, keep the rotor nice and tight, oil the roller and grease the folding handle and they work well. If your using your reel down then treat them carefully or they will end up scratched to hell. The mgs is made of magnesium which apparently can react to sal****er. It's what swayed me towards the aluminium model and bonus was they are or were cheaper.
I've noticed the mgs has come down in price and the xsc costs more in some shops. There are often bargains to be had if you look on the carp forums. If you have mates who want them you can often get them in 3s and split them between you to save a few quid!
I have a shimano bullseye for heavy ground and the gearing on that is superb. Its a lower ratio so has even more winding power. Again it's a metal framed reel which imo is what you need to prevent squirming and rotor wobble. Bullseye is like a metal ultegra and just as light. You can get them from Japan in a few days for around £150 ish, just ask the seller to put a low price on the customs declaration or you may get stung for import duty. The spool sits on a plastic line guard which makes you think the spool and rotor is flexing on the shaft but it doesnt seem to cause any issues.
With any of the shimano reels be careful locking down the drags, you must hold the spool and not overdo it or you can strip the threads on the shafts.
Other than the price I don't think you would be dissapointed with any of the high end shimanos. I can't compare them to spinfishers but my pal had one and wasn't impressed as he was with the battle and conflict.