Anyway, the decision between a 4200 and one of the 4DTVs is mainly a decision about whether you want to subscribe to pay services. You can't get a 4200 authorized (well technically it's possible, but no-one will do it). So you can only receive things that are free, ie FP or ZK. The advantage of a 4200 is that it can tune any frequency and/or SR, whereas with the 4DTVs, you can only tune things that are mapped, or at least that is my understanding, as I don't have a 4DTV (actually, I think you may be able to lock the carrier, but can't change channels).
Right now, there are a reasonable number of DCII subscription channels, but that is getting smaller and smaller, and if the subscription things go away, I'd rather have a 4200. However, my main reason for having a 4200 is for PBS programming, and a good bit of that is going away soon too. So bottom line, I'm not sure that I would recommend anyone to pay much for either a 4DTV OR a 4200, since the future of DCII isn't certain. However if you can get one cheap, it will get a few things for a while.
HOWEVER..... if you get a 4200, make sure it is a 4200V not a 4200b or 4200c. The "V" version gets all the SR rates, while the "b" and "c" versions just get some of the SR values. Unfortunately, most of the 4200s you see on ebay are "b" versions, and the "v" versions go for about 4 times as much.
When I bought my 4200V, it cost me nearly twice what I could have gotten a 4DTV for (both new). But my reason for getting it was completely to get PBS programming, and at that time the 4200 could get significantly more PBS channels than a 4DTV could. Even though the national PBS is leaving DCII, I think some of the local PBS, like Nebraska, Oklahoma, GPTV, LaPTV and others will stay DCII, at least for a while, but probably all will eventually go DVB.