I have a few old saws I bring out over and over again... One is, "There is nothing more expensive than a cheap fix." The seem to be yet another clone, like OpenVox, and the like. And like OpenVox, you may need to do some shoving to make them fit. So, some questions...
1) Is this a proof of concept that will be rolled out to many locations? If this is a one time only thing, you are risking both the money for the card, and the time to make it work.
2) Do you have a lot of free time to tinker?
3) Is this for production, right now? (You already answered this one, but others reading later did not)
If the answer to any of those three is "No" just get a well known and well supported card. Less risk, less time to make it work, and more people able to help.
If all three are yes, give it a shot and let us know how it turns out!
And I know this is not an answer to your question, but it may answer a few from people finding this in a search...
I want to second Lee's comments. Cheap is all well and good until something goes wrong. Something WILL go wrong, sooner or later.
In the end, you should answer these two questions:
1.) How much money will you save by buying the knock-off cards?
2.) How much money will your business lose while your phone system is down because the knock-off card is not fully compliant?
If #1 is greater than #2, then go for it.
I know that you mentioned using these for failover, and you therefore think "reliability isn't as important, they won't be regularly used." This isn't really true, as you need something reliable more than ever when your first line of defense has failed. If your main card fails, you have your backups, right? If your backup fails, what do you have?
I have a Sangoma card for this reason. I have always been thrilled when calling them for support. They are available and knowledgable. Well worth every penny.
PS: This isn't just hypothetical, either. I know a fellow who bought a similar card from eBay recently and he has been banging his head against a wall for ages because the cards are not fully compatible with DAHDi, so they require a patch, so you need to recompile Dahdi, etc, etc, etc.
Bought a card 3 months ago. No patch is required. It is fully compatible with the standard dahdi driver. In Elastix, I just do Hardware Detection. Bingo, all the ports are installed. It is effortless to install. It has been working great; no echo, no latency, no static noise. It also comes with 2-year replacement warranty. Their online agents are very helpful & knowledgeable. So I think that I would like to share this pleasant experience.
I have a few cards. 2 cards with 4 FXO modules and 1 card with a FXS module. The tech support is top notch and in fact they turned me on to Elastix.
The cards do well and auto detect like the last poster said.
I bought their TDM410P v2 cards, which use a 8 pin rj45 to two 2 port rj11 modules (see creame colored cable in this picture)
I use the FXS card to connect 4 lines to an IVR running some billing software on analog lines.
The 4th port off the cable on the FXS card was not working. I replaced that with a self crimped cable (RJ45 modular plg on a cat5 split to two RJ11 modular plugs with lt orange/orange as line 1, lt green/blue as line 2, lt blue/green as line 3 and lt brn/brn as line 4) and all works well. Except that line 3 and 4 seems to leak voltage somehow on a disconnect when you disconnect all lines at once, so my billing software running a dialogic card doesn't detect the disconnect. That line will eventually timeout in 10 seconds of inactivity on that IVR so its not a big deal. If callers dont't disconnect all at once lines 3 and 4 seem to disconnect fine.
I plan to buy at least 1 more card, so I will report here if I encounter the same issue on that one.
I am sure the techs would have helped me if I asked them about the cable issue, but it was a very fast fix for me.