Magnet sounds exactly the same as the TV providers we have in our development (soon to offer broadband, but I wouldn't hold my breath).
If you've bought an apartment and signed a leasehold agreement, you are more than likely prohibited from using dishes, aerials etc., so your choice of cable company is restricted (i.e. you cannot get Sky Digital or NTL through MMDS).
The situation is this-while the developers still control/manage the site, they have the right to grant exclusive rights to the site to any particular cable company. This is what happened in our development, and anecdotal evidence (from people I know who have bought apartments recently) suggests that it is becoming more common. I think the reason is probably cost, i.e. these cable 'resellers' offer to provide the connection boxes, wires etc. to each apartment at a cheaper (or free?) rate than NTL/Chorus, and so the builder can say that each unit is 'wired for cable TV' in the marketing spec.
We had to pay an €80 'connection fee' (some guy flicked a switch in a box downstairs) to get this service, and since there is no other option (well ok, rabbitt ears or no TV), I'm pretty sure every other apartment has this service as well.
Well these guys are cowboys. They were carrying Sky One and Sky News for around 4 months, until they figured out they didn't have a licence to do so, and now we are without both (no Simpsons at 7 makes for an unhappy CC), and we have seen no sign of Sky Sports (promised from the outset, which has led to CC spending more time in the boozer watching footie, early morning tips accross the city to watch the Lions, and an unhappy gf due to CCs frequent absences). Add to this the fee increase (concurrent with loss of Sky One etc.) and patchy service, and constant lies/fobbing off about Sky etc. makes for one crappy service.
However, when the developers hand over the site to the management company, we have the right to get whatever cable service we desire (as long as they supply us). The managing agent has said that NTL have now wired up to the entrance, and is ready to come on board whenever they are entitled to.
So bottom line is, Magnet Networks, good or bad, you probably have no choice for now!