Heart Rate Monitors - How To Choose

[Dubz]

Please excuse the long post, but it's complicated...

Note: I've edited it from my earlier post because I got more information since then.

I'm using TrainerRoad and have a Bontrager Duotrap S speed / cadence sensor which is Bluetooth and ANT+ compatible. I've decided that I need to think about getting a HRM for use with TrainerRoad and outside. I think it will help me to make sure that I'm not overdoing (or undergoing) my training.

Having done some research, I'm considering getting the ANT+ / Bluetooth compatible Mio Link HRM (Wristband). I've decided that I don't want to use a chest strap. Has anyone tried one this HRM?

Now I'm thinking about whether a bike computer is worth buying or not, since I could theoretically use an app like Strava on my iPhone 5S to track speed / cadence and heart rate. If I was to use Strava via my iPhone 5S only, would I need a Wahoo ANT+ dongle and a 30-Pin to Lightening adaptor as well? This is because I have a feeling that I can only connect one device via Bluetooth at once (e.g. the HRM). Could I then connect another device simultaneously via ANT+ (e.g. my speed/cadence sensor)?

Or if I buy a bike computer, can I get one that will pair with both my HRM and speed / cadence sensor simultaneously (via ANT+, I presume)? Would I be able to download the info to an app like Strava later?

Are there any computers that you recommend? I would want to buy something decent, but not too expensive. I realise that if I get the Mio, then I need to rule out Polar, as Polar technology is propriety.

Cheers.