Problem with analog PTSN cards in Asterisk

Hello, I write bachelor thesis about Asterisk and VoIP and I have in critism of opponent question: What kind of problems is with existing analog PTSN cards for Asterisk. I found, that analog cards make only Digium - TDM400 and 2400, Zapatatelephony.org and voicetronix . Here in Czech Republic are in the markets only Digium cards. So I need know, what same problems is with TDM cards. No problems like " is hard to configure" :smile: But problems like " This card is wrong designed, and shutdown the server every 12 hours" :smile: I hope, that I exactly say, but my english is not very well. Thanks for answers.