In reply to The Patriot:
Have you thought about getting a Bluetooth HR strap instead? That might allow you to remove the dongle from the equation entirely.
I had a Garmin HR strap and bought a Wahoo TICKR one instead, so that I could do some stuff with it with my phone, without having to have a dongle. From reading the Drivo blurb, sounds like it's equally happy on ANT+ or Bluetooth. I think the Wahoo HR strap was about £25 when I bought it, but it's more expensive now. (Guessing that if your phone has a Lightning connector, it's new enough to do Bluetooth Smart.)
Regarding rollers, I have the cheapest, most just-bits-of-plastic, no-resistance, no-electronics, Elite rollers (think the actual model name is Arion). They're good fun; mostly use them for when I've not been on the bike for a few months, to get some short saddle-time. I'd otherwise have to fight through stop-start traffic/lights to get anywhere interesting, only to turn around because my bike legs aren't up to any interesting distance. I feel that they've definitely massively improved my ability to balance on the bike and hold a straight line, and possibly even some pedalling smoothness benefits too.
The rollers are good fun, but don't think they'd replace a turbo, certainly not the no-resistance model I have. The maximum power I could achieve on my rollers was about 500 watts which was ~110rpm cadence with a 'speed' of about 60kph. The limiting factor was spinning out in the top gear, due to lack of any resistance. (I now no longer have a power meter on my bike, and don't have a turbo.)
Edit: To clarify, the TICKR strap works with my phone (over Bluetooth) and my running watch/bike computer (over ANT+), simultaneously if need be.
Post edited at 17:13