A TR is a decent idea if you are doing a lot of work and/or are inexperienced or out of practice. Few torques on a bike are critical after all. A few people get very hung up about torque values, in any quoted value there is an acceptable range, say 10-15Nm. Anywhere in this range is OK. In the quoted example of 5Nm and every bolt done up tpo that value, if that's what the manuf says then that's correct and doing so is absolutely correct. 4 would be equally OK, or 6.
Things get more critical around engines but as the engine in our case is fuelled by porridge and sausage sandwiches, it's not likely to overheat and cause a bolt to fail if it expands.
Decent torque wrenches do not have to cost £150. A 5 minute search of the net will bring up Britool ones at £70, these are absolute pro spec items suitable for full time mechanics or assembly lines. Decent ones for home use range around £20-30 and I do not agree with the poster who says a cheap one is worse than useless. They are great tools.