I've been running Showcase since forever... and switched to ShowcaseStandAlone a month or two ago due to the original one becoming unsupported. It works very well, I have noticed a little client-side FPS lag when you're near a lot of shops (due to the fixed, floating entities) but it's not a problem. We had a lot of players' shops all in one place, so we decided to redesign the market spread out over more space. This seems to have solved the (tiny) lag issue.
I recommend this plugin for Bukkit servers. But for Tekkit servers, I recommend the IC ShopOmatt machines. No need for an economy and shop plugin as the IC mod has them all built in along with coin items.