We use NPS methodology to administer this situation which is based on 2 constructs: likelihood to recommend and likelihood to continue to purchase. Google Net Promoter Scores - it might help you to understand "satifaction-loyalty" relation better.

Thanks, Himanshu

NPS seems to be better for testing brand/company loyalty. What about the situation for deciding on a new product if considering only the design feature but branding effect?

Hi Cheng - Hung Lo,

When it comes to new (or not yet introduced to the market) products, the literature often promotes the use of choice modelling or (as an easier alternative) contingent valuation methods. Essentially both methodologies break down the 'new' product into component parts and essentially ask respondents to make a choice based on different product specifications of the product. these component parts of the product (price included) could either be tangible attributes, or intangible policy initiatives. there are examples of either cases in the literature.

Hi Cheng-Hung Lo,

I'll second Alexandros '  suggestion.  Your case seems to be a text book case  for discrete choice modeling (DCM).  In DCM you can define your product based on as many attributes as you want, including  price, packaging etc and then derived the model based on the respondent's choice. The model is based on Random Utility Model and estimated as Limited Dependent variable Regression Model, in which the dependent variable is the choice and  modeled as (typically) Multinominal Logit. There are many literature available , a good book to start is  "Quantitative Models in Marketing Research" by Franses and Paap (Cambridge book).  In regard to your concern about  "the real cost of money" , DCM may have a good answer for that since it can be done through a "Revealed preference" in which the choice is observed in a real-life context (e.g. store-observation, scan data or pre-purchase interception survey) . There are some complexity in doing this, most importantly in defining the choice set but there are ways to solve that problems.  The method is quite widely used in Transportation (choice of transport mode), tourism and also marketing (product choice or store choice).  I hope it helps and Good Luck !